Hum in Parasound HCA 800 II

Picked up a used amp for my small home studio and it seems fine except for a very slight hum through the headphones.
I just set it up last night and have not tried it with speakers yet.

It has a two prong power cord and I have tried different outlets. I have disconnected the RCA ins and unplugged all devices near it. Still get the very slight hum. You don't notice it when you are playing music.

The hum does not increase or decrease in volume when I increase or decrease the level controls on the front of the amp.

Any ideas are welcome. I will see if the hum is present when I pick up some speaker wire this afternoon and connect the speakers.

Thanks for your help.

This is a power amp, right? And it has a headphone jack?
No surprise there is a hum thru headphones, which are very sensitive.
Yes, it is a power amp that has XLR to RCA inputs from my Mackie mixer.
Going to get some speaker cable right now to see if the hum is present in the speaker line out also.
Thanks for the response.
Cheaper parasounds are notorious for a transformer hum. 2 ways to fix, most common is lifting the groud with a cheap adapter plug, which isn't an option for you, other is try a power conditioner, such as a Monster HTS-1000 or up. I had a Parasound that would hum ocassionally with no apparent cause, 90% of the times it was fine, and simply unplugging the unit for a few seconds and the restarting cured the problem.
Thanks for the input.
I hooked up the speakers using some cheap Monster XP 16ga wire I grabbed off the shelf.
No hum to speak of so far through the speaker line outs.
I will see how it goes at different times the next couple of days.