McIntosh hum problem

Any of you MAC people own a MCD 751 CD Transport and MDA 700 D/A Converter combo? I do and both hum, wondered if any others with same problem? The converter hums louder and MAC gave me a new power transformer for it, but did not help. The hum is from the units themselves vs. speaker hum. Any way to reduce the hum. Any advice appreciated.
Check with Frank Gow at - he may be able to help or steer you in the right direction - they sell and refurbish Mcintosh equipment and have done so for years.
Sounds like a ground loop.
Hi. I don't believe it has anything to do with the units themselves since they both do it. I would check grounding also (in your outlet wiring) and make sure that all points are connected to the same spot.
Are the Mac's on a dedicated circuit? If not you may want to look at whatever else is plugged into that circuit. Some dimmers and motorized devices sometimes can be culprits. Especially suspect would be anything with a high/low switch in it. I had a room humidifier with said high/low switch and it made my velodyne subwoofer amp hum in the low setting.

Try unplugging suspect devices to see if you can locate a source for the hum.
Do they still hum when plugged into another outlet in another room? Have you tried cheater plugs on the units? Is your cable TV near these units?
It is ground noisy, Try use ground lift outlet(amp,D/A)
you can find at home depot or hardware store.
It is gray color , about fifty cents each. -good luck-
I tried different outlets, cheater plugs and no change. Units are in a different room well away from cable TV. Seems to be a problem with noisy power transformers. Thanks to all for your advice.
Those transformers should not be that loud. You need service as a problem prior to the transformer hooup may be creating the noise.
Thanks Ligi for the advice !
If you've narrowed it down to a transformer hum, try to find which circuit the amplifier is running off of. Then check the circuit breakers in the service panel.

Chances are that your amps' circuit is on the opposing phase of some of your other audio circuits and therefore generating some AC noise thats affecting the transformer. Have an electrician move all of your audio circuit breakers in the service panel to the same phase of 110 volts.

I moved all dedicate audio circuits to the same phase and that cured my transforer hum.
Thanks for the advice Stehno and I will check this out.
Amwarwick, I would be very interested in your findings.

When I made this change, I was simply trying for some/any sonic improvement. Did not notice any, but I was quite pleased to discover that the amp's transformer hum disappeared.

Pleas keep me posted.