One of the pins on the LM386 can be used as a squelch by grounding
it.  The question is whether or not the LM386 draws much current in that
mode.  If I remember correctly, the pin is normally just bypassed to ground
with a .05uF capacitor or sometimes a larger electrolytic cap, but it will
shut the LM386 down if grounded.  In a circuit I built about 10 years ago,
I used an open-collector output on a logic chip to mute the 386.  You might
use a resistor to make the dropping of the pin to ground a little less
abrupt than it would be if one just connects it directly to ground.  I seem
to recall that the thump you get on the LM386 is a little less loud if the
pin goes down gently.  Look for a RC constant of per haps .1 second or so
to soften the thump.  I don't remember how much current the LM386 draws in
this mode, but it was a fraction of normal idling current.  Since the mute
pin is supposed to already be bypassed, you will only need the resistor to
tie it to the open-collector output on your PIC.  Normal audio is with the
output high while a short to ground or a low mutes the 386.

Martin McCormick