What kind of CPU do you have ?

Should be able to handle it.
When the sounds to lag, are there pieces being skipped or played with a pause in between.
So if we take the word "pause"
would it be
p.... se
or
p.au..se

It might be difficult to tell though.

You aren't running a Bittorrent client at the background or something like that ?
Did you check if the windows updates have been succeeding ? As those get retried in the background if they fail, which can give bad performance.