A question for PMDG Queen developers

Hi,I would like to draw the attention of PMDG developers on the following behaviour of the Queen. I am not pointing out it as an issue, but I would like if possible an explanation.I have a high end PC (AMD 4800+, ATI X1900XTX, 2 Gb RAM, ecc..), and I usually fly in VC. I have the indication of FPS enabled, and what I notice is a cyclic oscillation of FPS from 30-40 to 15. This must not be confused with the typical FS9 fluctuations of FPS. What I am describing is a standard solid rate of say 35 FPS suddenly dropping to 15, without any evident reason (no scenery change, no weather change, no ATC communication), remaining to 15 -16 FPS for a few seconds and then returning to 35....staying there for another minute or so and then the cycle starts again. This is not depending on the complexity of the scenery (3d clouds or addon airport do not influence the "cycle", they just reduce the maximum level of PFS but the cyclic fluctuation is still there).I have a pretty clean machine, FS on a different HD than the Operating System, everything is defragmented, the registry is clean, no CTD at all..the sim is very smooth and it is a real pleasure to fly the Queen....it is just this fluctuations which is very annoying expecially if occurring during take off, approach and landing...Am I the only one experiencing the issue ? Can PMDG explain what is causing this and/or suggest any fix or troubleshooting ?Thank you