Check that you don't have any audio effects like stadium or tunnel, etc. loaded, there were problems for some with those back in the W7 Betas.
whoops didn't read that last part-
I had a program installed called DFX Audio Enhancer
that was very clearly affecting performance - no doubt it sounded great, but when I swapped to speakers from a headset, I couldn't really hear a massive improvement so I uninstalled it, plus I had heard that DPC latency issues affected Audio/Video playback, and that effects (DSPs I think they are called - eg W7 sound effects / DFX Audio Enchancer) can cause these issues.
So yeah I would have totally agreed with you there, but when I swapped to a USB wireless stick, I still get a small(er) lag spike when connecting/disconnecting from the internet, plus the DFX program was long since removed. So I'm not so sure about it being wireless drivers. There is a possibility that MorphVOX is to blame.. it uses voice effects (great fun
) so I'm sure it uses DSPs as well.. I'll try disabling it and see if the lag spikes occur.