Hey GB,
never mind that other post and comments.....
Well, after 10 + years ??? Obviously there is nothing else in your system or your behavior that induced the noise, as the amp ran perfectly after a decade plus...
In your case and looking at how you describe it, it's probably the capacitors....caps can get old, and I usually advise changing power supply caps every 7-10 years. They can dry out, not holding a charge or get noisy when charging up.
You know what, best thing is to email me through the web site, and I'll help you out,
Klaus