Nak PA-5 is buzzing ???

I have a Nakamichi PA-5 amplifier. When it warms up, there is a very audible "buzz" or vibration emitting from inside the amp. It sounds like it originates right behind the front panel. The amp plays well and sounds good, but something isn't right.

I live out in the boonies and there isn't a shop for hundreds of miles that I would trust to look it over. I'm hoping something expensive isn't worn out.

Thanks in advance for any input you may have.
Probably the power transformer. Some are very prone to mechanical humm or buzzz. Pull the cover; if the transformer is right in front, then thats the problem. Often can be very difficult to correct, unfortunately. Some folks have had luck with Audioquest AC filters.
Swampwalker is correct the massive power transformer in the PA-5 is in the center mounted directly behind the front panel. If you can not here the hum/buzz from your listening spot don't worry about it. I use to have a PA-5 in the late 80s-90s. It likes it's power direct from the wall outlet, unfiltered..

I have been reading through the archives, and am thinking that maybe I am not getting enough power. I plugged into a different outlet and the buzz has nearly gone away. Hmmmmm.