lots of problems indeed. but possibly all related.
I'd be looking into a power supply issue in regards to the display being weird. check the DC voltages and make sure they aren't low... but also check those voltages with your voltmeter set to AC...this will tell you if there is ripple in the voltages. I would suspect anything over 25mvAC on low current DC rails and around 100mv AC on the high current ones indicating the filter capacitors in the main power supply/amp board aging and needing replacement.
since this amp is also powered by the same transformer assembly as the rest it makes sense you hear noise from the amp if this is the case.
the computer in these machines is VERY susceptible to power fluctuations. if the power is dirty, it will do all kinds of things...reset...freeze... it has to be clean power.
the CD mech typically just needs to be cleaned. there are quite a few optical sensors...if they get dirty, it's will get lost in it's multi step procedure to move the trays in and out. you have to hand it to the germans for over engineering the crap out of things to make them stupid complicated.