Vanishing and Buzzing sound from a laptop

Do you have a question? Post it now! No Registration Necessary.  Now with pictures!

Hello group
Just recently  one laptop of mine while running  and playing a video ,
its sounds just  turned to buzzing/humming sound .
It started when I plugged in my USB external  hard drive, video that i
played just turned  the distinct video sound into a buzzing  or
humming sound.
When I removed the external hard drive  , it did not  sort the problem
and the buzzing sound persist even when the PC was  restarted.
When I did a system restore to an earlier point in say about a few
days ago, the sound quality  returned to normal.
I can't find any reason or explanation for this peculiarity , does
anybody of you guys know why and how this  behavior occurs?
That laptop is almost 4 years old but never had an audio problem
since  but just that sudden peculiarity I experienced now...
BTW I did not see any error noticed provided by the windows this keeps me wondering....
 I never experienced it before but only lately and this time only?

Site Timeline