Sudden fps drop while on the ground

Hello guys, there must be a similar post discussed with this issue, but I'd like to note here with my case.I'm using i5 [email protected], 8G, 9800gtx+ and most options were set very low. (no autogen, water 1x, no traffic, no ASE, no REX)All tuning for FSX has been done, too. (including aff mask.)I always fly with default airports and the fps always shows more than 40+ (without fps limiters)But rarely, fps dropps about 5-15 only inside of VC. I don't know why this happens from time to time, but I found a fixed condition.Happens once in 10 flights. (about 10%)This fps drop only STARTS WHILE ON THE GROUND. Doesn't matter the airport at departing airport or destination.If there were no fps drop until I started pushback, it never happens until I get landed.I flew so many times since NGX has released, this issue started it's RTM through SP1.Even occurs network unplugged and I removed automatic update and defrag schedule.It is hard to find the answer because can't capture image or record memory status but I'm sure few people reported this before.Wish there would be improvements with SP2.