Strange sound for no apparent reason

Just recently I have started to get the sound that is usually played in association with closing programs/applications but it happens lots of times as if something is happening in the background but nothing shows in the task manager although the order of programs keeps changing quite rapidly.
As far as i can tell it is not affecting performance but it sure is annoying,,the only way I can silence it so far is by turning the system sounds slider down to 0.
I have used several different malware scanners to no avail and also some other tools.
I hope someone here can help me get to the bottom of this annoying problem.

Thanks in advance

No, It is nothing like the USB sound that you mentioned,,,,the only thing i can find in control panel settings is the sound that is normally associated with closing a program,. But like I said it seems to happen extremely frequently and also for no apparent reason.
I think that there could well be some well hidden malware somewhere that is causing this although so far none of the scans that I have done have came up with anything.

I hope someone can help me get to the bottom of this annoying problem.

No difference,
Scans I have done are as follows.
Malwarebytes Anti Malware and anti rootkit
SuperAntiSpyware
Emsisoft
RogueKiller
TDSSKiller
ASWMBR
AdwCleaner

If you would like me to re run any of these I will be more than happy to do so although I do think something else is causing the problem,,either that or something that hasnt been recognised yet as nothing seems to shopw up.