computer audio ground loop hum--any suggestions?

I recently installed a new power supply in my desktop. Everything works, but I have acquired what sounds like a ground loop hum in the speaker with the on/off switch and volume control (and the hum gets louder as I turn up the volume). There is no hum in the other "satellite" speaker. The power lead from the woofer unit only has a two-pin plug on it, so there's no chance of using a "cheater" plug to life the ground, although it seems as if that wouldn't have worked anyway.

Any suggestions?

(FWIW, the wiring scheme is pretty standard. A lead with a stereo minijack takes the two-channel audio from the back of the CPU to the back of the speaker with the on/off switch and volume control. Another thicker lead from the back of the speaker goes down to the "woofer" with a multi-pin connector going in to the woofer. A second thinner lead coming out of the same multi-pin takes audio out to the other "satellite" speaker. A separate power cord from the woofer goes to the power strip.)
Can you try reversing the plug (flipping it 180)?
Also try re-dressing the cables.
My usual suspect (coax CATV) seems to be in clear on this one.
Are the computer and the speakers plugged into the same power strip? If they are not, and particularly if the power strip has a surge suppressor or rfi filtering built into it, the resulting isolation could conceivably be the cause.

The other thing that comes to mind, which once caused me to have a similar problem, is simply poor contact between the mini-plug and the mini-jack. With the volume control on the speaker set fairly low, try jiggling the plug and see if that affects the hum.

My feeling has been that 1/8 inch mini-connectors, and also 1/4 inch headphone jacks, are abominations. Unfortunately, they seem to be unavoidable these days.

-- Al
One other thought -- does your computer have one of those cheap little plastic microphones plugged into it, the kind that are intended for dictation? I've found that they are very prone to hum pickup, due to their lack of shielding. If you have one connected, either unplug it, or mute it in the software that controls your sound properties.

-- Al
Many thanks to all! Some vigorous jiggling of the miniplug, and some careful dressing of all the cable runs, seem to have done the trick! Much appreciated.
Your welcome. Great "moniker"!