Tom, it does sound heat related. I would call McIntosh, they are very good at helping you diagnose and also in the past they done repairs for me, and although out of warranty, it was still free. I just paid the shipping to them and they sent it back at no charge. Not saying it is policy, but worth a try.
They never indicated it would be free before I sent it, it just worked out that way. They are a great company to work with.
They never indicated it would be free before I sent it, it just worked out that way. They are a great company to work with.