PSS 757 - Help with FPS spikes and stutters

Hi everyone

I have the PSS 757 (bought from Just Flight as 757 Professional) and have decided to reinstall it after a few years without using it. Everything works fine, except for a small detail: every few seconds, my FPS "spike" down - I'm locked at 60 and they go down to 50. This doesn't seem much, but it's enough to cause a noticeable stutter which is very annoying. I've tried with lower fps locks, but the same happens (40 going to 30, etc).

I searched around for similar problems and fixes (removing the VC, lower EFIS settings, etc) but having tried them there is no change, so I'm assuming they're not causing the problem. Also, the spikes happen in every view, inside or outside.

Has anyone had and was able to fix this problem, or might otherwise suggest an approach to fixing this?

Running FS9 (of course  ) in Win 7 64-bit, ATI 5870 card, latest FSUIPC and AIRAC cycle.

Any help would be much appreciated.

Cheers

Antonio