Sorry for the delay in replying on this issue.
There are two possible reasons that I can think of for this issue.
FxSound process not getting enough cycles to process the audio samples on time. For this you can try increasing the priority of FxSound process in Task Manager.
Any other audio processing application also is running which is causing the latency in the audio samples to reach FxSound. If there are any other such applications running, you can exit them and try.