I've been experiencing a weird buzzing problem on my MIJ Fender Marcus Miller 4-string... when I play a 'D' (7th fret - G string) and a 'B' (7th fret - E string) at the same time, I get a buzzing noise. If I play either note by itself, no buzz. Funny thing is that 99% of the time it only happens at the 7th fret. So, I took it to a tech and he tightened my neck... then it started to buzz on the 7th, 8th, 9th, and 10th frets too. He told me that it was the truss rod that was buzzing inside the neck and that there was no remedy. So when I got home, I loosened the neck a little bit so that it would only buzz on the 7th fret. The buzz doesn't come out when I plug into an amp so at least I can still play it live. It's just really annoying. Is the tech's diagnosis correct? Any other theories?