Will study all these suggestions. Many thanks! I was getting the hum (just realized) with TV input selected only and will look at maybe a missing ground where the coax comes into the house.
Chasing 60 hz hum
I have an MC 7150 and an MC 7104 in my system, both plugged in to the same circuit on a power strip. The problem is that McIntosh went away from two prong and moved to 3 prong grounded wiring when the 7104 came along. I also moved from a C39 to an MX119 preamp, again the change from ungrounded to grounded. Having these units together on the same circuit produces a nice fat 60 Hz hum. To cure this, I used cheaters (3 to 2 adapters) on the 3 prong devices and this works.......mostly. Then, every few months the hum comes back and I go to the strip, wiggle one of the adapters a little bit and it stops....but this is a pretty goofy way to run an otherwise nice railroad....anyone got any ideas that are not radical (such as rewire the house!)