
As a general rule, no relay will cleanly switch audio if you try to tranfer
the circuit with the contacts.  The noise you hear is due to the momentary
opening and closing of the path.

The noiseless way of transfering audio is to ground the circuit.  In high
impedance audio circuits a resistive "T" is constructed close to characteristic
impedance of the circuit.  Grounding the imputs (connected to the T) transfers
the audio.

In low impedance circuits transformers are usually used, and the inputs are
shorted out or grounded.  Secondaries are paralleled at the characteristic
impedance.

Sometimes if it is necessary to actually switch audio, a second contact is used
to momentarily short the circuit output for the duration of the switching time.

Telephone relays are handy, because contacts can be adjusted to "Make before
break and Vica Versa" but I haven't seen any of these for years.

Nowadys switching is done electronically with OP amps, etc.

A novel circuit I used to build was a primitive "optical isolator".. It consists
of a resistive photocell and a lamp, all packaged in a tube.  When the lamp is
off the cell is high resistance.  Turn the lamp on and the resistance lowers
passing the audio.  Once again this device in a "T" switches the audio.  Varying
the lamp resistance give a remote volume control.  Use 2 variable resisters and
you have a mixer!

Lots of luck!
-- 
73, Tom
================================================================================
Tom Wagner, Audio Visual Technician.  Malaspina College Nanaimo British Columbia
(604)753-3245, Loc 2230  Fax:755-8742  Callsign:VE7GDA Weapon:.45 Kentucky Rifle
Snail mail to:  Site Q4, C2.   RR#4, Nanaimo, British Columbia, Canada, V9R 5X9  