your audio circuitry caps are leaking. I've seen these symptoms on three different a4000 boards, two of them which died on me cause I was late to act. third one I could save by timely replacement of all SMD caps. As far as I understand, these caps are at the end of their life and should be replaced ASAP when you get a a4000. There's no way around it. And it's not that difficult. I could finish a whole board in about an hour after getting used to it and have the parts ready (and I should mention I'm not tech wizrd).
