Crackling sound

Its strange, I also have crackling sound in FSX. I don't have any sound problem when playing music or other game.Last night I uninstall FSX and reinstall. Just before I install Acceleration, I ran FSX once along with Latency Checker, wow very very low latency and no crackling sound at all. Latency Checker show all green bars, I didn't even see a yellow bar! So I thought reinstall will solve the problem. Then I installed Acceleration. Guest what? Right after installation, I ran FSX. The high latency came again, Latency Checker fill with red bars, and crackling sound "join in" when I fly. Why? Any idea?