The following are some reasons that could lead to the Pioneer FH x700bt no sound issue:
Bad connections
If there are electrical glitches in the wiring, it can cause the unit not to work.
Wrong antennas
If an antenna is not set up properly, then it could cause interference and result in the Pioneer FH x700bt no sound issue. This is typically a problem with outdoor antennas. In order to fix this, you will have to recalculate your broadcasting strength and check if there are any obstructions in between the device and your antenna.
Old firmware
In some cases, outdated firmware might be the reason behind the Pioneer FH x700bt no sound problem. It is important to periodically update your devices so that you avoid any possible issues caused by outdated software.