rumbish

Hi everyone. Today i realized sudden problem in my A6 2005. I switched radio and there was loud noise from the sound system. I thought it is because bad radio signal and i switched to CD. And the same problem - loud noise like from old radio. Somewhere in this noise i could barely hear the song, but it was realy barely.

And if i anderstand,this noise comes only from rear speaker. If i remember,front speakers didnt switched on at all.

Please,help me someone with some advice. I dont wanna go another time to the AUDI service (