As a follow up to this post two weeks ago, it’s pretty obvious that the issue I was experiencing was caused by Bitdefender.  Since switching back to using Kaspersky I’ve not experienced any slowdowns or abnormally high CPU or interrupt usage.

This is unfortunately since until I ran into this problem I had been quite happy with Bitdefender.  I’d read some of the horror stories about Bitdefender’s quality control but I had chalked them up to the usual combination of overblown edge cases with wonky configurations and disgruntled fanboys.  I can’t say for certain when this issue was introduced and I have to assume that it doesn’t manifest on every system or else it would be much more widely reported, but either way it’s serious enough for me to abandon paid software and buy a competing product.