P4PE Overheated CPU Symptoms

I have the following system:
•P4PE/LAN/1394/SATA-UAY
•Pentium4 3.06GHz / 533MHz FSB
•512MB PC2700 DDR333
•NVIDIA GeForce4 MX440 128MB (A-G446)
•Midi Tower Case with 350W PSU

The problem is ten minutes after powering on my computer, it starts
beeping with short high frequency sounds during a scroll operation in
an Internet Explorer webpage or other CPU intensive operations
(playing videos, games, etc) as it is mentioned in the manual for
overheated CPU problem. Strange thing is normal operations like
browsing the file system, running simple applications (like text
editor, emailer or MS Office) or even editing pictures (in Photoshop)
don't trigger any sound.
I watched the temperature with Asus Probe and MBM and I've got 32
Celsius degrees for the case and 38-55 Celsius degrees for CPU. The
Intel datasheet (ftp://download.intel.com/design/Pent...s/29864311.pdf)
says the temperature range should be from 5 to 69 Celsius…
Anybody solved a similar problem? Please help.

TIA,
Aegyssus