Sounds like you solved your buzz...
Another one to look for (happened to me a year ago). Same thing... a noticeable, not loud twangy kind of buzz appeared after a string change. But only with certain notes (frequencies). Initially with a capo on... and I spent some time looking to see if it was back buzzing strings (strings behind the capo vibrating and hitting frets...). I get that sometimes, 'cause I have the nut slots on a couple of guitars cut reeaaaal low... Anyway, that wsn't it.
I spent close to half an hour plucking and listening, trying to figure out where it was coming from. Finally decided it was up coming from near the nut/peghead... real frustrating. Finally, I found it...
Turned out to be one of the cut tag ends of a string was resting against one of the strings running from a tuning peg to the nut. At certain frequencies, it would vibrate against the other string and buzz. Now, last thing I do after changing strings, tuning, etc, is to look at all the cut string ends and bend them up slightly at the peg so they don't touch any of the other strings running from peg to nut.
Dave