Hashing Rate jumping around

[Nemesis099]

I'm new to mining and I did some searching but I couldn't find any information on what is happening.

My has rate has been jumping around from as low as 180 to as high as 420 MH/sec on a Powercolor HD 6950 using stock settings, the gui miner (no extra commands) in windows 7 with BTC Guild.  My second and third card of the same type doesn't jump around like this at all as far as I can tell.

It seems to typically hover in the 280 - 300 MH/sec range but the large jumps and dives are starting to make me wonder what is going on.

Sorry if this question was posted before I did search but couldn't seem to find anything.

Thanks!

[Reckman]

Try removing windows aero, and adding -f1 or -f10 flags