Random radio noise

I have a RR 2002 HSE. Since yesterday the radio start sending a pretty loud noise to the front top speakers and after a while it stop by it self. I was thinking that it could be some kind of frequency entering the radio through the emergency alert or NDS but when it happened there is no change in the display of the radio. As I read it should be a message that said alarm or news in the display if it is one of those two. Anyone with a problem like that? I have to listen to the radio with the fade to the rear speakers to avoid listening that noise. :doh:

Also I notice that when the music stop, the noise also stop.

Now the noise is there all the time, no audio from the bass speakers on the front. Look for the amp. inside the door but never found it. Anyone knows where it is? The only box that I saw was the outstation but no amp.