Amplifier Hum

I have a Classe CA-100 that I just purchased and there is a loud hum when I turn on the amp. My previous amp was an Acurus A100, which also had a hum, but not nearly as noticeable. What are some of the root cause of this hum? I assume it is electrical interfernece, but I am not sure from where. Any help is greatly appreciated.
some causes are:

Loose or incorrect transformer mounting.

DC voltage on the line. Does the hum vary at different times of the day? Do you hear it through the speakers?

Here's info from people who want to sell you a power conditioner to fix hum: Finding and Fixing Hum
Might be your preamp. I had amp hum once. I changed preamps and it went away. The hum was only noticable when the preamp was turned off.
I had amp humm and initially thought it was the amp. Turns out, Toroidal (sp??) transformers are prone to this as a result of electrical interference. In my case, it was a halogen lamp on the same circuit as the amp. Turned off the lamp, away went the humm.

My current amps do humm slightly due to design, not a big deal though.

Even number of grounds? Dimmer switch on the same circuit?
Try using a "cheater plug" on the amp (converts from
three-prong to two-prong). Often a hum is due to
a ground loop and floating the ground will eliminate
the hum.
I too had a hum problem. T began by turning off my source components, still a hum, then my preamp still a hum. Tried a diffeent amp, still a hum. Changed out the cables from the amp to preamp hum was gone.
Though sometimes the hum might be just because it doesn't know the lyrics. :)
Check the A/c plug on the back of our amp...if there's a 3rd prong on the unit, that is more than likely the cause of your problem. The extra conector will generate a 60 hz cyle humm which may be coming through you cable TV...try disconnecting your cable vision and see if the problem does away. I had the same problem and the culprit was my cable which was not properly grounded. Unfortunately, the only workaround was to buy a cheater plug (which as I understand can be a fire hazard), OR purchase a Jenson transformer ground loop isolater. I picked one up off Ebay a few months ago for 50 dollars and the problem was solved immediately. Here is the part # VRD-1FF and here is the website to lern more about the product

Good luck
TDSPEP11, I just verified your AMP on the Classe website and it does have the 3rd connector which may be causing the ground loop problem that I refered to above. Again, try disconnecting your cable as a test.
What's hummin'? The amp, or is the hum coming out of the speakers when the amp is on?

If it's the amp itself, check your grounds and try the old process of elimination by removing other stuff on the circuit. Can't really add anything to what's been said already.

If it's through the speakers, (again) definitely try the cable -- especially if you had the same problem with two amps -- as it don't sound like the amp(s) are to blame at all. Ground loop hums off of a coaxial cable line are very common. If you have a cable line running anywhere into the system (or anything even remotely connected to the amp) I'd bet you dollars to doughnuts that's your culprit. If that's indeed the problem, Radio Shak makes an coaxial RFI blocker that's mean to fix just that sort of problem. Bought one, didn't work worth a damn. Useless. Mondial also makes a "magic block" that's supposed to do the trick. It'll cost you $100, though (which, all things considered, is far more cost effective than a $20 Rat Shack paper weight that doesn't work -- or even weigh enough to hold down paper). Finally, as mentioned by Senoir Rudd, there is also the Jensen VRD-1FF -- which worked like a charm for me (and made me very happy). And if it doesn't, they'll give you your $60 back. Best of luck.
Thanks everyone for all of your input. This has helped me nail down the problem. It does appear to be interference from the cable. I will look into the Jensen isolator recommended by Rudd and Mezmo. Thanks again.