Strange sounds...

Hi there! I have a strange problem on my desktop at work. If I use my headphones to listen to music, there is noise or some sort of feedback that occurs evertime I move my mouse or type on my keyboard. I've never encountered anything like this before.

I have a Dell 933MHz Xeon with Win NT4 SP6a. I use an HP Internet keyboard and HP mouse. I installed the software and drivers for them, but the sound/noise is still there. Nothing appears to be wrong with any of the audio devices (in Control Panel, System) and the Audio Card is seated firmly in the slot.

Does anyone have any idea what is causing this noise? It is driving me crazy and I cannot use my headphones, even if I need work done.

Thank you in advance for any assistance you may provide.

Ken