I've done such for clients and the hours you rack up is costly. But here's what we do. We not only compare what you noted which is nothing but a clue that something software is different but is a clue that some program, setting or infection has caused this.

This is not an offer to teach computer forensics but to share that you would look at all the running programs (preferably right after a reboot to narrow it down) and see what's different.

I'd also take Grif's advice from http://forums.cnet.com/5208-6122_102-0.html?threadID=328220#2968150 (same advice applies to this and other issues.)

Good hunting,