Dealing with transformer hum

My Belles 150 makes a humming/vibrating sound which I'm told is due to the transformer. At average listening levels, the hum is not an issue at all, because it's not loud enough to be heard, but I do a lot of really low level listening at nights, and this hum is driving me absolutely nuts.

I don't have the option of really moving the amp much and there are no enclosures to hide it away in. Any ideas?

Thanks in advance,
I had a Belles 150a Hot Rod that annoyed me mightily with the same problem. The toroid transformer in these amps are very easily excited by noise pollution in the ac lines. I found that when fans or certain ac appliances would turn on in the house (not on the same circuit) the amp's toroid would start humming. If your hum is intermittent, you might see if there is any correlation between appliances/ac/etc. operation and the hum. Perhaps ac power treatment would help, or maybe you just have an amp that's going to hum. When I talked to Dave Belles, the owner of the company and designer, he basically offered no help and admitted that the amp was prone to this peculiarity.
Photon46 is right on the mark. I have a Belles 150a hotrod which also had an intermitant transformer hum which I eventually tracked down to a humidifier on the other side of my apartment. Took me forever to isolate this. Before I figured this out I did try an AC power conditioner which solved the problem although I did feel it constricted the amp somewhat. I should add, hum issue solved, that I think this is a great amplifier. Good luck!
As mentioned, many appliances set off the humming. Even though I have dedicated lines from a separate sub-panel, I still hear the hum whenever the microwave is used. Other motors and appliances do the same. Worst case, you may need to go to a line conditioner of some sort -- preferably one that attacks both small amounts of dc voltage that could be in the line (you could check that) and the spurious high frequency noise that is part of our AC system.
I've got to agree. Mine hums if the dryer is running (I told my wife I'd beat her if she does THAT again!), microwave, etc.... I don't like to use a power conditioner with this amp. It normally sees duty as a sub amp, and the hum is never noticable there.

But, now I've got it hooked up in my main stereo system so I can track down a problem with my Audio Note amp. Mated to the Supratek Syrah with 93db AN speakers, any noise on the amp end comes through.

Admittedly, it's a pain in the A@#, but I do like the amp. So, I just have to be careful to schedule my listening time when the old lady's not home to turn shit on and annoy me! FWIW
My rig uses short paths throughout run from pole to meter base/through dual dedicated to units(less 40')second breaker after a/c,yet I heard torriodial humming late evening when the noise floor drops.
Tracked it down by throwing breakers off line one by one. Narrowed down the offending circuits,outdoor lighting transformer,toothbrush charger,cheap radio,refrig. So now I just throw those breakers off,when turning on the audio breakers.Ahhh ,the details emerge from a black hole now!
Interesting ideas. I don't know how thrilled my parents will be at me cutting off their electricity for my late night listening sessions. Hopefully they have some candles nearby or something. I kid.

Thanks for all the input. Like most Belles users, I really love my amp, save for this one annoyance that I can hopefully solve.
I have some Quiet Line (by Audio Prism) on order as my dealer recommended placing these on the same outlet as my refridge (which causes a humming/hiss in my speakers) and he also said anything ciruit that has a motor in it... so I'll have one on each outlet for my stereo and one in every circuit in my house to help keep things as quiet as possible.

I had hissing and crackling in my speakers and tracked this down to my computer equipment (that's what I do for a living so I have tons) and I researched it hear on audiogon and some people suggested putting my Ultimate Outlet in front of my computer equipment to keep it from poluting my ac lines, and sure enough I stuck it before my UPS and suddenly I had quiet, I have a little bit of tube hiss right now that I didn't have on another circuit in my house so I can't wait to put the Quiet Lines in to get to that next level.
I had this problem with Cary monoblocks once. FIND THE LIGHT DIMMER IN YOUR HOUSE! When the lights were dimmed, meaning resistance in the AC line, the transformers would buzz like crazy. That was the problem for me, anyways! Good luck!
Actually, the reason the transformers hum is because DC is getting on the primary of the transformer.

Here is a little quote by the one and only Nelson Pass (my hero) :

"If you are experiencing mechanical hum from your
transformer, it is often caused by the presence of
DC on the line. Usually this comes from some appliance
using current asymmetrically, such as a lamp dimmer.

The hum comes usually from toroidal transformers, which
saturate easily with DC, and when they recover, they
draw an extra pulse of current, causing the noise.

You can put a pair of back-to-back electrolytics in series
with the AC power line to block this, and it works fine.
Makes sure the current rating of the electrolytics is
high enough, and the they are joined at a like polarity,
such as + to +."

If you trace the hum to the transformer you may want to give the above suggestion a try. I insert two back to back electrolytics on the primary in every amp I build as a matter of design, so I never have to worry about this type of caveat.
Liguy, I'm not exactly sure what these electrolytics are of which you speak? Can you recommend a brand or a site I can look up to learn more about these. They sound very promising.

All good thoughts and if they relieve the problem , great , but if all else fails The Ah Offset Killer works very well. I had tranformer hum with a Rotel, then with an Anthem. Ive upgraded to Classe since then and the Classe is dead quiet, but I remember The previous Amps tranformer hum driving me off the wall. If you do a search on google it leads you in the right direction.
There are a couple of things causing transformer hum in my sytem. My RPTV casues a slight amount of hum when turned on, and when my wife is using the blow dryer or curling iron I get a LOT of hum, even though those devices are being used on a completely seperate circuit. I'd be very interested in more info on the "electrolytic" solution as well.
Go to the psaudio web site as they have a interesting product just for hum, it's called the humbuster. Also lots of info on the subject!
Here's an interesting reference to the Nelson Pass comments and a lot of discussion around hum circuits. You may have to join the diy site (which is a pretty cool place) to see the circuits themselves -- there's a link to get to the original posts and, after joining, you can see the attachments. BTW, the scope pictures of dc and transformer saturation at the end is very instructive -- I loved the comment "a 60Hz transformer is basically a big, heavy bad antenna" (that may not be an exact quote). Here's the site: