Unwanted sound when recording in AA3

I am getting a hum or buzz when I click the record button in AA3 (see attached). It only appears when recording in A3. I am now using an M-Audio Mobile-pre temporarily (replacing a dead Delta 66). Any thoughts would be greatly appreciated. Here are the computer specs:

Audition 3.0 build 7283.0 [Audition\3.0]
OS Version: Windows XP [5.1.2600] Service Pack 2
Intel IPP: ippst7l.lib v4.0 4.0.19.77
Cache Size 32768 K
There are 2096620 total Kbytes of physical memory.
There are 4142580 available Kbytes of page file.

Audio Device Info
----------------
Multitrack View Driver: M-Audio USB ASIO Interface
   Buffer Size: 256
   Inputs: 3
   Outputs: 3

   Input Port: [01S] Line In 1 MobilePre
   Output Port: [01S] Analog 1/2 MobilePre

Edit View Driver: M-Audio USB ASIO Interface
   Buffer Size: 256
   Inputs: 3
   Outputs: 3

   Input Port: [01S] Line In 1 MobilePre
   Output Port: [01S] Analog 1/2 MobilePre

Surround Encoder Driver: M-Audio USB ASIO Interface
   Buffer Size: 256
   Inputs: 3
   Outputs: 3
Monitor : \\.\DISPLAY1 (PRIMARY)Device : RADEON 9200 SERIES   
StateFlags : desktop primary
Display Rect:
   left : 0
   top : 0
   right : 1024
   bottom : 768

I don't know what's causing that sound, but it's unacceptable.

I tried four tests on my own system, and here are the results:

1  Au3 with no preamp hooked up.  The meter jittered at -78 dB during playback.

2  Au3 with a preamp hooked up and turned on.  The meter jittered at -72 dB during playback.  So, the pre added 6 decibels of noise to the recorded track, but it wasn't anywhere near as audible as the sample you posted.

3  CEP 1.2 with no preamp hooked up.  The meter jittered at -81 dB during playback.  This was the quietest.

4  CEP 1.2 with preamp.  The meter jittered at -72 dB during playback, just like Au3.

The reason I A/B'ed Cool Edit and Audition was because I wondered if the extra resources that Au needed somehow generated more noise that my onboard soundcard would pick up.  If you compare results 1 and 3 above, it looks like Au adds 3 decibels of sound, but if you compare 2 and 4, it looks like it adds nothing.  The results seem pretty inconclusive, but I have to emphasize that what I produced on my system wasn't anywhere near as noisy as what you're getting on yours.  I'm running an M-Audio Delta 44 card on my machine.

Thanks for the effort, Dobro. I still can't figure out where this is coming from. However, I have replace the Mobile-pre with an M-Audio Audiophile 9426. So far, no noise.

I wonder if the position of the USB cable would affect the signal.

How were you powering the Mobile Pre? It is possible that the USB suplly was rather noisy. Did you try it in a different USB socket? Or alternatively run it through an externally powered USB hub?