[EDIT - CRISIS AVERTED I took the neck off and tightened the trust rod and the buzzing has stopped for now] I have a loud sympathetic vibration/buzzing on my newish-to-me 80s Fernandes PJ, and I'm worried that it could be a truss rod. I'm wondering how to deal with it. I bought this bass about a month ago. It's got a heel-adjust truss rod that I've avoided dealing with so far. It came with light strings, and when I got it, I replaced them with Fender 9050ML flats. It sounded good and the new strings didn't cause the neck to bow unreasonably. Then, the other day, I put new pickups on the bass. When I loosened the strings to put the pickups on, I broke the G string. I replaced the strings with 45-105 Boomers. After playing them for a little while, I began to notice a buzzy rattle. It sounds like it's coming from the headstock, but it could be the neck. I checked all the tuners and they seemed OK. I tightened some screws, but it didn't seem to rattle less when I put my hands on them, and everything seemed pretty tight. It also didn't seem like it was coming from the pickup/electronics cavity, which I suspected because I'd been changing pickups, etc. Eventually, I dropped the tuning a step down to D and the buzzing stopped. Today I changed the strings to 9050Ls (i.e marginally lighter than the Fenders I'd had on before that didn't cause any problems at the time), and the buzzing returned with a vengeance. Once again, if I drop the tuning, the buzzing stops, or at least is reduced.. What do I look at now?