I have a 2007 Toyota Avalon Limited. For the last three years or so I get a very loud cracking noise from the Radio, I can even turn it off and it continues or gets louder. I took it to the dealer, they think it is some of the speakers. Since are 12 speakers, not sure I want to start replacing them. I thought it might be the amplifier, took to an electronics guys. He took a lot of the car around the radio apart, we could never find the amplifier. I think the amplifier is in the trunk with the GPS Disk Player. If you were going to replace something, would be the radio, amplifier, or? The only way to stop it is to remove the fuse which causes the radio and GPS screen to not work.
It is usually a failing amplifier that causes the rhythmic popping. When it is making noise unplug and reconnect the amplifier to see if it temporarily becomes quite.
The Amp usually does this
This is a third vote for a bad amp.