audio signal muting

[zzattack]

My car speakers output a loud popping noise when the headunit turns on/off. In this headunit the pre-amp signals are connected in parallel to the internal amplifier.

I believe the internal amplifier is instructed to mute during poweron/poweroff conditions, thereby preventing the noise. Does that make sense?

Clearly the pre-amps are unaffected by this muting. I can think of 2 ways to fix this, but am unsure whether these actually help.
1) I could add a FSA551 analog switch to disconnect the pre-amp signal from the RCA outputs. If we detect the muting condition then we can use that to drive the switch.

I'm unsure whether this would work, because I don't understand the cause of the popping noise. If instability in the supply net causes noise on the signal lines, then wouldn't the analog switch suffer the same noise causing similar noise to be generated on the 'disconnected' pre-amp?

2) Second alternative would be to quickly disable the upstream devices by pulling their remote enable signal low. This will probably work if the upstream devices turn off fast enough, but they seem to stay on for about another half a second after cutting its enable signal. So I anticipate this would only reduce the popping noise and not eliminate it entirely.

Any advice?

[ssashton]

This might help give you some ideas -  http://sound.whsites.net/articles/muting.html

You probably want to read the section on JFET muting circuits which are muted when the power is removed / un-mute when power is on. Other type of circuits usually need power applied to enable mute, which means you need the circuit to enable when you switch the head-unit off and I assume that is impracticable.