High Frequency MB Noise - USB Audio Interface Picking Up Too

High Frequency MB Noise - USB Audio Interface Picking Up Too: "

I built two systems at home last years using the same following components on each:

- Intel BOXDG43RK LGA 775 Intel G43 HDMI Micro ATX Intel Motherboard
- Intel Core 2 Duo E8400 Wolfdale 3.0GHz LGA 775 65W Dual-Core Processor BX80570E8400
- Kingston 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1066 (PC3 8500) Dual Channel Kit Desktop Memory Model KVR1066D3K2/4GR
- MASSCOOL FD08025S1M4 80mm Case Fan
- Sony Optiarc CD/DVD Burner Beige SATA Model AD-7260S-01
- Western Digital Caviar Blue WD2500AAJS 250GB 7200 RPM SATA 3.0Gb/s 3.5' Internal Hard Drive

I'm using the on-board graphics, network, and audio (e.g. no other cards installed). The only difference between the systems is one has a more powerful power supply, but the problem I'm experiencing is noticeable on both systems. Running Windows XP SP 3

I am wanting to use one for a digital audio workstation (DAW) and have purchased a Behringer UCA202 USB Audio interface to plug in my mixing board to for this purpose. The problem is I'm getting a very high-frequency humming through the "monitor" port on the Audio Interface. (I have very sensitive hearing and can actually hear this "hum" just by putting my ear to the back of the case/motherboard.) I have tried everything I can think of to get rid of this noise, but most improvements are minimal. I finally decided the Behringer interface must be bad, but I tried it on two other systems at work (a notebook PC and a desktop PC) and the background is totally silent. Therefore, there must be something in the chipset / processor / memory / power supply configuration that is causing this high-frequency oscillating sound.

I would greatly appreciate any ideas...

Thanx

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