Hmmmmm... I'm fighting a similar battle right now. I only fly CFS2 and I've just purchased a new pc... a Dell 4600C, 2.66GHz with 64mb NVIDIA video card.

The problem I had (have) is more noticeable if the aircraft is parked aborad a carrier with the engines shut down. Normally, you should hear the dull roar of the carrier, especially in external view. Instead of that, I was getting this annoying buzz... it seemed to come and go... like you said, sounded like something wasn't grounded. Every now and then, the normal sound would pop in there but mostly, it just sat there and buzzed. I also noticed that if I panned around outside the aircraft, I'd get an occasional video stutter.

Everyone I talked to seemed to think the problem was being caused by my sound card acceleration settings. While taking the acceleration all the way down did help, it didn't cure the problem.

After trying a few basic things with the pc, I decided to monkey with my settings in the game. First, I turned the hardware accleration completely off. When I fired up the game, my frame rates, obviously, were miserable; but the sound problem was cured. I reactivated the accleration function and decided to look into some other things.

Next, I checked the box called "Anti-alias" and started the game again. This seemed to help a lot but I still had some sputtering. Next, I checked T&L and fired the game up again. The problem was 99% resolved.

While this took care of the problem, my frame rates dropped (because of the anti-alias deal) from about 77fps to 38 fps... but I can deal with that if I have to. Now, I'm flying combat with anti-alias off and fun flying with it on (the buzz isn't as noticeable with all the sounds of combat around you).

This is more of a patchwork solution as opposed to a real fix. I'd like to know how to get this problem resolved... THE RIGHT WAY. If you find out what's causing your problem, let me know. By the way, what kind of sound card are you using?