peculiar fan sounds

[rajatQ2]

hey there,
this isnt really a problem, but i find it a bit funny.

every time my processor is under any sort of load, i can hear the fan speed drop down. its pretty funny.
So , if i scroll my wheel mouse button through a GotApex forum web page, i can hear my fan speed drop down.

has anyone else seen this? could it not be my fan spinning at all?
i have a p4 1.8 ghz dell machine, maybe 6 months old now.

[Markel]

A similar thing started on my system when I changed the power supply (from a 300W to a 400W). The fan in the 400W is louder than my 300W was, and I get the "audible load sound effects". But I think my pitch gets higher as the load increases.