[G3 Q&A, Help & Troubleshooting] sireebob:
While some are better than others, I can't find any ROM that is stable, stock or otherwise, on this thing... This might be a 5.1.1 AOSP issue though.

My vs985 just did this for the first time on Paranoid Android (AOSPA Legacy), Aug 22 2015 version (5.1.1), which I've been running without issue for a few days (until now). It has impressive sound quality with the phone speakers right out the gate, and I was listening to music with them.

It was a loud, fairly high-pitch, constant drawn out beep while I was listening to music in Songza and trying to choose a photo as my wallpaper. The first thing I did was try to lower the volume but discovered this had no effect at all on the volume of the tone. Then, I tried to pause my music, but I don't think that helped either. It did stop after 15 seconds or so, but I am not sure if it was because of anything I did. There was nothing in the notification bar to indicate this was an intentional alert, and I was on Wi-Fi only in airplane mode.

I have a Cool Tool HUD which didn't seem to indicate a high temperature or other things to cause problems -- at least not that I noticed. CatLog did have some errors like this:

08-30 08:21:00.374 E/ACDB-LOADER(304): Error: ACDB AudProc vol returned = -19

...but I get those even when it is working fine. I didn't catch the time down to the second when it happened and it is hard to parse through the log. It's so full of errors and warnings as it is.

I did see entries in the log about Google Now Launcher activating its hotword detection. Doing stuff with my wallpaper could have meant a bunch of activations and deactivations of mic input as I went to and from the launcher, in case that was somehow related.

Did get these, too:

08-30 08:21:18.968 W/AudioService(892): stream was not muted by this client
08-30 08:21:18.968 E/AudioService(892): Could not get client death handler for stream: 1
08-30 08:21:18.969 W/AudioService(892): stream was not muted by this client
08-30 08:21:18.969 E/AudioService(892): Could not get client death handler for stream: 2
08-30 08:21:18.969 W/AudioService(892): stream was not muted by this client
08-30 08:21:18.970 E/AudioService(892): Could not get client death handler for stream: 5
08-30 08:21:18.970 W/AudioService(892): stream was not muted by this client
08-30 08:21:18.970 E/AudioService(892): Could not get client death handler for stream: 7
08-30 08:21:18.971 W/AudioService(892): stream was not muted by this client
08-30 08:21:18.971 E/AudioService(892): Could not get client death handler for stream: 8
08-30 08:21:21.331 E/AudioTrack(892): AudioTrack::set : Exit
08-30 08:21:21.342 W/msm8974_platform(304): Codec backend bitwidth 16, samplerate 192000
08-30 08:21:21.342 W/msm8974_platform(304): New codec backend bit width 16, sample rate 48000
08-30 08:21:21.402 W/msm8974_platform(304): Codec backend bitwidth 16, samplerate 48000

This is weird, too. 192000 sample rate?

08-30 08:21:00.138 D/audio_hw_primary(304): out_set_parameters: enter: usecase(0: deep-buffer-playback) kvpairs: routing=2
08-30 08:21:00.183 I/Timeline(892): Timeline: Activity_windows_visible id: ActivityRecord{2d064ec3 u0 com.google.android.googlequicksearchbox/com.google.android.launcher.GEL t347} time:102015929
08-30 08:21:00.235 W/FlurryAgent(29454): Trying to end session
08-30 08:21:00.250 I/sf_frame_dur(276): [SearchPanel,4,2,0,0,0,0,0]
08-30 08:21:00.332 I/sf_frame_dur(276): [com.ad60.songza/com.songza.activity.PlayerActivity,15,0,0,0,1,2,25]
08-30 08:21:00.353 I/HotwordRecognitionRnr(2014): Starting hotword detection.
08-30 08:21:00.356 I/MicrophoneInputStream(2014): mic_starting com.google.android.apps.gsa.speech.audio.u@2d7f5daf
08-30 08:21:00.357 D/audio_hw_primary(304): adev_open_input_stream: enter: sample_rate(16000) channel_mask(0x10) devices(0x80000004) stream_handle(0xb1833ac0) io_handle(3652) source(6)
08-30 08:21:00.362 D/audio_hw_primary(304): in_standby: enter: stream (0xb1833ac0) usecase(7: audio-record)
08-30 08:21:00.362 D/audio_hw_primary(304): in_standby: enter: stream (0xb1833ac0) usecase(7: audio-record)
08-30 08:21:00.362 I/AudioFlinger(304): AudioFlinger's thread 0xb1dca000 ready to run
08-30 08:21:00.364 D/audio_hw_primary(304): in_set_parameters: enter: kvpairs=input_source=6;routing=-2147483644
08-30 08:21:00.365 I/MicrophoneInputStream(2014): mic_started com.google.android.apps.gsa.speech.audio.u@2d7f5daf
08-30 08:21:00.374 D/ (304): Failed to fetch the lookup information of the device 0000003E
08-30 08:21:00.374 D/ACDB-LOADER(304): ACDB -> ACDB_CMD_GET_AUDPROC_COMMON_TABLE
08-30 08:21:00.374 D/ACDB-LOADER(304): ACDB -> ACDB_CMD_GET_AUDPROC_COMMON_TOPOLOGY_ID
08-30 08:21:00.374 D/ACDB-LOADER(304): ACDB -> ACDB_CMD_GET_AUDPROC_GAIN_DEP_STEP_TABLE
08-30 08:21:00.374 D/ACDB-LOADER(304): ACDB -> AUDIO_SET_AFE_CAL
08-30 08:21:00.374 D/ACDB-LOADER(304): ACDB -> AUDIO_SET_AUDPROC_CAL
08-30 08:21:00.374 D/ACDB-LOADER(304): ACDB -> AUDIO_SET_AUDPROC_VOL_CAL
08-30 08:21:00.374 D/ACDB-LOADER(304): ACDB -> send_adm_topology
08-30 08:21:00.374 D/ACDB-LOADER(304): ACDB -> send_audio_cal, acdb_id = 62, path = 1
08-30 08:21:00.374 D/ACDB-LOADER(304): ACDB -> send_audtable
08-30 08:21:00.374 D/ACDB-LOADER(304): ACDB -> send_audvoltable
08-30 08:21:00.374 D/audio_hw_primary(304): select_devices: out_snd_device(0: ) in_snd_device(61: handset-mic-vr)
08-30 08:21:00.374 D/audio_hw_primary(304): start_input_stream: enter: stream(0xb1833ac0)usecase(7: audio-record)
08-30 08:21:00.374 D/hardware_info(304): hw_info_append_hw_type : device_name = handset-mic-vr
08-30 08:21:00.374 E/ACDB-LOADER(304): Error: ACDB AudProc vol returned = -19
08-30 08:21:00.374 I/msm8974_platform(304): platform_send_audio_calibration: sending audio calibration for snd_device(61) acdb_id(62)
08-30 08:21:00.378 I/sysui_heads_up_status(1353): [,0]
08-30 08:21:00.379 D/audio_hw_primary(304): select_devices: done
08-30 08:21:00.464 I/HotwordWorker(2014): onReady
...
08-30 08:21:03.004 D/audio_hw_primary(304): out_standby: enter: stream (0xb587f980) usecase(1: low-latency-playback)
08-30 08:21:03.032 D/hardware_info(304): hw_info_append_hw_type : device_name = speaker
08-30 08:21:03.610 V/GOOGLENOWINTERCEPT(2049): Type: 2048;ClassName: android.widget.LinearLayout;Id: com.google.android.googlequicksearchbox:id/page_indicator;Text: null
...
08-30 08:21:10.240 W/FlurryAgent(29454): Ending session
08-30 08:21:10.724 E/AudioTrack(892): AudioTrack::set : Exit
08-30 08:21:10.734 D/audio_hw_primary(304): select_devices: out_snd_device(2: speaker) in_snd_device(0: )
08-30 08:21:10.734 D/audio_hw_primary(304): start_output_stream: enter: stream(0xb587f980)usecase(1: low-latency-playback) devices(0x2)
08-30 08:21:10.734 D/audio_hw_primary(304): start_output_stream: enter: usecase(1: low-latency-playback) devices(0x2)
08-30 08:21:10.734 I/msm8974_platform(304): platform_check_codec_backend_cfg Codec backend needs to be updated. new bit width: 16 new sample rate: 192000
08-30 08:21:10.734 W/msm8974_platform(304): Codec backend bitwidth 16, samplerate 48000
08-30 08:21:10.735 W/msm8974_platform(304): New codec backend bit width 16, sample rate 192000
08-30 08:21:10.741 I/ActivityManager(892): START u0 {act=com.android.systemui.recents.SHOW_RECENTS flg=0x10804000 cmp=com.android.systemui/.recents.RecentsActivity} from uid 10016 on display 0
08-30 08:21:10.742 I/am_home_stack_moved(892): [0,1,0,0,intentActivityFound]
08-30 08:21:10.742 I/wm_task_moved(892): [347,1,1]
08-30 08:21:10.750 I/am_home_stack_moved(892): [0,1,0,0,bringingFoundTaskToFront]
08-30 08:21:10.750 I/wm_task_moved(892): [357,1,1]
08-30 08:21:10.753 D/hardware_info(304): hw_info_append_hw_type : device_name = speaker
08-30 08:21:10.755 I/am_pause_activity(892): [0,755388099,com.google.android.googlequicksearchbox/com.google.android.launcher.GEL]
08-30 08:21:10.759 D/ACDB-LOADER(304): ACDB -> ACDB_CMD_GET_AUDPROC_COMMON_TABLE
08-30 08:21:10.759 D/ACDB-LOADER(304): ACDB -> ACDB_CMD_GET_AUDPROC_COMMON_TOPOLOGY_ID
08-30 08:21:10.759 D/ACDB-LOADER(304): ACDB -> ACDB_CMD_GET_AUDPROC_GAIN_DEP_STEP_TABLE
08-30 08:21:10.759 D/ACDB-LOADER(304): ACDB -> AUDIO_SET_AFE_CAL
08-30 08:21:10.759 D/ACDB-LOADER(304): ACDB -> AUDIO_SET_AUDPROC_CAL
08-30 08:21:10.759 D/ACDB-LOADER(304): ACDB -> AUDIO_SET_AUDPROC_VOL_CAL
08-30 08:21:10.759 D/ACDB-LOADER(304): ACDB -> send_adm_topology
08-30 08:21:10.759 D/ACDB-LOADER(304): ACDB -> send_audio_cal, acdb_id = 14, path = 0
08-30 08:21:10.759 D/ACDB-LOADER(304): ACDB -> send_audtable
08-30 08:21:10.759 D/ACDB-LOADER(304): ACDB -> send_audvoltable
08-30 08:21:10.759 D/hardware_info(304): hw_info_append_hw_type : device_name = speaker
08-30 08:21:10.759 I/msm8974_platform(304): platform_send_audio_calibration: sending audio calibration for snd_device(2) acdb_id(14)
08-30 08:21:10.763 I/am_resume_activity(892): [0,327302496,357,com.android.systemui/.recents.RecentsActivity]
08-30 08:21:10.769 I/am_new_intent(892): [0,107288318,357,com.android.systemui/.recents.RecentsActivity,com.android.systemui.recents.SHOW_RECENTS,NULL,NULL,281034752]
08-30 08:21:10.769 I/am_task_to_front(892): [0,357]
08-30 08:21:10.775 I/am_on_paused_called(1855): [0,com.google.android.launcher.GEL]
08-30 08:21:10.780 I/HotwordDetector(2014): Closing mic
08-30 08:21:10.785 I/MicrophoneInputStream(2014): mic_close com.google.android.apps.gsa.speech.audio.u@2d7f5daf
08-30 08:21:10.796 I/am_on_resume_called(1353): [0,com.android.systemui.recents.RecentsActivity]
08-30 08:21:10.809 D/audio_hw_primary(304): in_standby: enter: stream (0xb1833ac0) usecase(7: audio-record)
08-30 08:21:10.837 D/hardware_info(304): hw_info_append_hw_type : device_name = speaker
08-30 08:21:10.838 D/audio_hw_primary(304): select_devices: done
08-30 08:21:10.877 D/hardware_info(304): hw_info_append_hw_type : device_name = handset-mic-vr
08-30 08:21:10.888 D/audio_hw_primary(304): adev_close_input_stream: enter:stream_handle(0xb1833ac0)
08-30 08:21:10.888 D/audio_hw_primary(304): in_standby: enter: stream (0xb1833ac0) usecase(7: audio-record)
08-30 08:21:10.890 I/HotwordRecognitionRnr(2014): Hotword detection finished
08-30 08:21:10.891 I/HotwordRecognitionRnr(2014): Stopping hotword detection.
08-30 08:21:10.953 I/Timeline(1353): Timeline: Activity_idle id: android.os.BinderProxy@2b26ce93 time:102026699
08-30 08:21:11.085 I/Timeline(892): Timeline: Activity_windows_visible id: ActivityRecord{13823d60 u0 com.android.systemui/.recents.RecentsActivity t357} time:102026831
08-30 08:21:11.100 I/sf_frame_dur(276): [com.google.android.googlequicksearchbox/com.google.android.launcher.GEL,293,25,0,6,2,1,1]
08-30 08:21:11.122 D/audio_hw_primary(304): out_set_parameters: enter: usecase(0: deep-buffer-playback) kvpairs: routing=2
08-30 08:21:11.303 I/sysui_heads_up_status(1353): [,0]
08-30 08:21:12.126 E/AudioTrack(892): AudioTrack::set : Exit

I know this is just a Q&A thread and not a place for ROM support necessarily but putting this info elsewhere is too much work at the moment. This thread was the top relevant forum search result for the issue.