It has been suggested to me by Ralph Karsten that the problems you describe could be the result of RFI contamination of your environment. The only part of your story that gives me pause is that the problem seems to show up after warm up. I don't see a tie in between that and RFI infiltration. However, I believe you stated that you live in an apartment which could surely be awash in RFI based on poulation density and neighbors using all kinds of computers/electronics with SMPS, etc.
I just wonder if there is any chance you might have a failing powwr supply capacitor in amp or source that begins to fail after a period of usage/warmup. I'm by no means a "tech" guy but it sounds like you are losing drive.
I just wonder if there is any chance you might have a failing powwr supply capacitor in amp or source that begins to fail after a period of usage/warmup. I'm by no means a "tech" guy but it sounds like you are losing drive.