Hello all, new guy here. A bit of background... been playing off and on for 35 years, more "on" recently. For Christmas I got my first 7-string, a lovely Schecter Hellraiser Hybrid C-7. What an instrument, I already love it. I got it from Sweetwater and had them set it up with NYXL 64-11 strings. Enter the issue. I have a metallic "ringing" occurring only when I do percussive palm muting on the E string. It does not happen then I do the same thing on a different E (e.g. on the B string). A perfect example: the intro to Pantera's "Walk" (I know, it's in D but imagine it transposed to E). When I play that bendy F to E and mute the strings right and left handed there's a bright, metallic ring that occurs for maybe a tenth of a second. It is acoustic (you can hear it even unplugged, though you have to listen carefully) and is amplified quite awfully. Many of you will immediately say "sympathetic vibration behind the nut" and you'd be partially right. There was behind the nut vibration which I've now damped in various ways, from a hair band to a truly drastic and ugly sock under the strings and wrapped twice around the headstock to really damp it all. That got rid of much of the behind-the-nut sound... but there's still a ringing chime left. The next common wisdom is tighten everything down which I verified. After that is typically "check your pickups/put foam under pickups". I removed both pickups (separately) and they both already have nice foam underneath and no springs, and the sound persisted with the pickups completely removed. Next felt like the Hipshot Hardtail and perhaps resonance of the springs. I damped the springs -- and even removed two of them temporarily -- to no avail. At this point I'm not quite at a loss. I feel like the only two remaining possibilities are: changing the strings (which I'm loathe to do given they're brand new strings) and applying some kind of damping to the strings where it goes through the body. That last one is my final best guess. Perhaps that part of the E string where it goes through the body is getting some kind of sympathetic resonance that's transmitted through the body or bridge. I suspect it is the E string because when removing the pups I tried reproducing the sound with the rest of the strings fairly slack. Any other thoughts?