RPC service causes CPU frequency to drop to 0

Hi there, I have already posted this in other forums but noone could help me, so I hope you guys can :D

Details of problem:
Here are some screenshots of the task manager ressource monitor:
http://i.imgur.com/7sJgMOJ.png, http://i.imgur.com/qspR3O8.png
As you can see, the CPU frequency drops to 0 for a short period of time, it looks like it shuts down and then jumps back to normal performance. This happens about ever 30 seconds to 1 minute. Everytime it happens, my whole PC lags and the video and audio begin to stutter for a few seconds.

Solutions and measures conducted:
Latencymon tells me there is indeed an issue as seen here: http://i.imgur.com/D106wIG.png, but no drivers could be identified as cause.
DPC Latency Checker confirms the issue here: http://i.imgur.com/SwgOPTX.png

I found out that the svchost process associated to the RPC services (Remote Procedure Call) is the cause. Its name is "rpcss". The system does not allow me to stop it, but if I crash the corresponding "svchost.exe" process, the drops stop, but it is a very important one and I cant use most PC features after doing that so that is no long term solution. I need advice on how to fix this.

Recent changes to hardware/software:
None.

System specs:
Windows 7 Professional 32 Bit, Intel i7 870 2.93 GHz, 4 Gb Ram, Nvidia Gefore GTX 460, Gigabyte Mainboard P55M-UD2

Thanks in advance!