Random lag periods with gmod

when i play garry's mod it runs fine, but every like 10 to 30 minutes i get this random lag and my fps drops to like 1fps for about 5 minutes. its starting to do it in my other source games now. HELP!!!! i know my computer can handle this game easily.

Computer info:
AMD Athlon 2 X4 620 Quad Core Processor
8gb RAM
1TB Hard drive
Nvidia Geforce 9100
Running on windows 7 home premium 64-bit

i think it might be wiremod but if it is why would it make me lag? please help, i cant play gmod without having this anoying lag.

What could be the problem?
 
I am betting against the 1TB drive... Is it a Seagate, Samsung, Hitachi, or Western Digital ?
 
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