I think I have an amp problem

Without having the unit in to evaluate it sounds like capacitors are failing in the power supply.  Open up the cover and check to see if they are bulging.  Check for any burn marks on the circuit board or if they have any smell.  This is a very simple check but after that it needs to come to a repair shop.  We are in New Jersey if we can assist you.

Happy Listening.

Have you made any changes to your system lately that may have an associated effect? If so, check he polarity of your cables, especially your speaker cables. If not, I would borrow another integrated to install and compare. Good luck!

zlone +1

If it's really input-specific and occurring on more than 1 source, start with the source control knob.  Cables are less likely to be the issue, for the same reason, but it's possible that multiple sets are failing.

If that doesn't solve the problem: the phono section takes a different path to the power amp circuit.  However, you could try switching the cables between the CD and streamer and preamp to see if the problem follows the cables or stays on the same source setting.

I would not play it until I was sure what the issues are ... that is a great amp!

@OP Given the age of the amp it is most likely to be a power supply problem. The effect you describe sounds as if the phase of the signal is being temporarily affected which could possibly be a power drop on the supply rail on one bank of push pull transistors. The nature of the problem and the age of the amp would suggest an immediate trip to a technician. A problem of that nature is only likely to get worse with worse consequences for the amp - and for your speakers if the amp goes DC.