From reading the comments and my own experience, this could caused be any of the problems found in any stereo since they were first built, room , grounding, impedence matching, shielding,etc. Its possible to get great sound from missmatched junk, and have mega expensive gear suffer from an out of phase conection, and be unlistenable. In another life, I was a sound engineer, and the place to start is with a known reference, ie :headphones ? do they still sound good on something else? Intermitent conditions can result in madness, but you got to have your tunes!