The white noise/fizz sound is very typical of the audio amp chip dying, typically a 5pin, 7pin (or more)..
Without knowing (or seeing) the schematic, that's my first thing to look at......maybe find the audio IN to that chip and listen to it to see if it's clean going into the amp to confirm.
Otherwise, it could still be any part of the chip(s) that make up various oscillators/noise-generators elsewhere.
MM
