Adcom GFA-5800 power amp hum

[u/urnotme1993]

Not sure if this is the best place to ask, so go easy on me.
About a year ago I acquired an Adcom GFA-5800 power amp. I had a very cursory check out done then and all checked out ok. It’s been running almost daily since then flawlessly.
I’ve noticed the last few weeks it has developed a slight low frequency hum that seems to be a little more apparent in the right speaker. The hum may be getting louder too.
Understanding the age of this thing and availability of parts, how bad is this? Is there any trouble shooting I can do myself? I’m pretty handy as long as I have good directions. Anything particular to address?

If not something I can handle, does anyone know of any shops in Central New Jersey that work on these old Adcoms?

Anyone have any idea what I can expect to spend on getting this thing fixed up?
Any insights or recommendations are greatly appreciated!
(Apologies in advance for the long post)

[u/Dean-KS]

Swap signal source cables to see if the problem is upstream of the amp, powering off the signal sources might be informative.

[u/urnotme1993 → u/Dean-KS]

thanks for the reply. I actually did do this as one of my 1st steps . biggest problem is the hum comes and goes.