What kind of noise do you have?

If it's spurious signals/carriers, then it might be that power supply! (that's
what mine did - generic 233mhz PC).

My powersupply used the power cord as it's antenna making my whole system of
power cords radiate the birdies. Ferrite cores did nothing to help me.

Grounding the PC case to it's own ground rod helped about 10db. That was
better, but still most of the AM band was shot.

What got rid of 99% of the carriers on medium wave, was to open the bugger up,
and put high voltage bypass caps from the rectifier to ground (.1mfd). I also
put the same caps from the power cord to ground, and then wrapped all wires
comming from the powersupply to various internal parts, around Radio Shack
ferrite cores.

I now only have a half dozen weak carriers on long wave and medium wave, and
they are only about S6 using an external antenna and now I can use my PC for
recording my DX sessions.

Unfortunately, you would have to have the shop open up both the computer and
the powersupply to modify it. Not sure if they'd do that for you.

Good Luck !

John Wilke
WB9UAI
Milwaukee