So, I discovered a few weeks ago that my plywood DB has an internal rattling sound whenever I play an A (of any octave). It's not a loud rattle, but it's loud enough that I feel the need to troubleshoot it. Here's what I have checked and eliminated so far: The rattle is only apparent when I play an A with moderate or higher pizz force. Quietly-played A's do not have the rattle. So, something inside the bass seems to have a resonant frequency of 110, 220, 440, 880Hz, etc. It's unknown if I get the rattle arco, as the sustaining of the notes would cover up the rattling sound anyway. End pin assembly: Everything appears tight and firm, at least on the outside Bridge and bridge piezo pickup: Nothing appears to move or shift Tailpiece and string ends: Everything appears to be solid Neck, figerboard, tuning machines: The sound seems to be coming from the body of the bass. Soundpost: A visual inspection shows no issues, but I'm really not an expert there. Does anyone have any ideas or suggestions for additional troubleshooting? Thanks in advance.