Aragon 8008x3 noise

I have an Aragon 8008x3 amplifier (and an 8008x2). When I switch the home theater system on, the 8008x3 is dead silent (as it is supposed to be). After the system plays for an hour or so, there is a low level but quite audible noise (sounds like a wavering flutter) which can be heard from the center speaker. This noise persists irrespective of the volume setting on the preamplifier and it persists even when the DVD player and the preamp are switched off. It disappears only when the amplifier is turned off. The noise can be heard only from the center channel (I have switched speaker wires from the center channel to the others and the noise shifts to whichever speaker is connected to the center channel output; so it isn’t the speaker.

Has anyone had this kind of a problem before and had it successfully fixed? All ideas appreciated. Also, are there any really good high end audio servicers you know of in the DC/VA/MD area?

Thanks!

Ashley