Strange CPU usage issue

[mulletgut]

Hi folks,
My computer has started doing a cyclic pause (lasts about a second every other second) but not all the time. The computer might be fine for hours of for just 10 minutes before it starts to happen.
As an example, if I'm listening to an mp3 I hear the song then each second a buzzing sound, or if I'm on skype the conversation is muted each second (both incoming and outgoing). If I return to desktop and move the mouse cursor it tracks but will pause each second.

If I close all applications and take a look at my task manager I see system Idle process 98 or 99% in the CPU column, but the CPU usage at the bottom of task manager says 23 or 24%.
When this weird pause thing isn't happening the CPU usage figures in task manager tally up correctly.

Does this point to an error somewhere which I don't understand?
Screenshot of my task manager whilst the strange cyclic pause is going

I have run memtest and found no errors.
There is no application starting which I can find to cause this. I can walk away from the machine with nothing running and come back an hour later and it will be happening.
I have tried shutting down network magic - no change
I tried shutting down Antivir - no change

Has anyone heard of this issue before?
Got any ideas as to what could be causing it?
Thanks for your time.

My machine is getting on a bit:
AMD 3000+XP
MSI KT3 mobo
1GB RAM
GF 6600LE
Pioneer DVD ROM
Pioneer DVDRW
Creative SB Live Audio
Netgear WGR614

Software:
O/S WinXP
Antivir Personal
Network Magic
I don't have a lot of other stuff running.

 

[webada]

did you follow mech's guide? its great, you should check for malware, spyware, etc. definitely use hijackthis. I got rid of many spyware/malware that AVG or ad-ware wouldn't remove/detect.

next thing is the latest and greatest windows update. make sure you disable automatic windows update, it sucks juice and causes lag.

 

[mulletgut]

Thanks for your reply.
I have run Ad-aware, Spybot S&D, Hijackthis, CCleaner and I don't have the lastest Win updates.
I know it is a strange issue, but I was hoping someone might have experienced a similar issue and could identify with the symptom.

 

[webada]

if you system is indeed clean, I would check the following:

1. Disable any autoupdates from every software (real, creative, logitech, antivirus...etc) all these periodically checks for software updates.

2. Check power managment profile, making sure you are set to always on.

3. Check CPU stepping, the feature is call powernow or cool n quiet. you should be able to disable this from the bios,

There could be a momentary lag when you are drawing more juice and your cpu is stepping up its power. Shouldn't be but could be a combination of your bios and amd driver not being updated.

 

[mulletgut]

After trying many things, I ended up re-checking all the power cables and plugs. I unplugged them and re-plugged them all checking for firm fit and connection. Since I did that, my problem has not resurfaced. Maybe it was a loose connection.