My Grandson was playing his stereo when all the speakers stopped...just a humming buzzing sound now...CD player still has power botn amps still have power..puzzled.
Make sure the system is off, and disconnect a set of RCA's. Turn on the system.
Repeat this until the noise goes away. If the noise goes away, said channel is the issue at the head unit. If the noise doesn't go away, problem is in the amplifier(s).