My radio makes a popping sound every 3 seconds which also freezes the volume control and heard it might be because a bad amplifier. I changed the spark plugs for the radio and amp and it worked for a little while now its back in full swing.
The service manual says it's in behind the right side kick panel in front of the passenger door (in other words below and to the right of the glovebox). But it says only cars equipped with the optional premium speaker system have an amp.