well I inspected the caps and replaced them: nothing
I think maybe it could be the headphone jack itself or the volume pot?
because the hum comes through the speaker and the factory headphone jack but not the prosound jack. plus the you can hear scratchiness when you turn the pot and when its set at the highest setting sometimes sound cuts out completely.
i thought maybe the batteries because I use rechargeables and they're old so I tried different ones same problem.