musical fidelity a3.5 amp hum

I bought a musical fidelity a3.5 amp recently. I noticed sometimes it hums. What the problem? any solution? thanks.:confused:

How loud is it? Do you have to crank it and get real close to the speakers to hear it?

Does it do it on all sources?

Does the volume control have any affect on it?

Hum is usually a ground fault problem. When you say it hums sometimes, does a hum happen when your using a specific source? If so then the SOURCE is the cause, not the amplifier.

Problem resolved. I check the information of the cd, that kind of low frequency noisy is from the breathing of the piano player. I used a cheap Amp before, I never felt so obvious. Thanks for the reply.