If temperature is involved this problem can be caused by noisy transistors in the input section of the amp. I've seen this a good number of times.
The capacitor failing didn't sound right to me as soon as I read it- if caps start to make noise, its usually pretty profound- the sort of thing that has you diving for the power switch- a bad cap can sound like arcing or something burning (which can well be the case).
The capacitor failing didn't sound right to me as soon as I read it- if caps start to make noise, its usually pretty profound- the sort of thing that has you diving for the power switch- a bad cap can sound like arcing or something burning (which can well be the case).