Thank you Rich.
The problem, on my boat, is that I can’t get to the area of the noise. I’ve disassembled shelves in the locker adjacent to the bed, but still have no access to the area of it. Likewise, at the other (stern) side of the headboard I removed the entire upper shelf, in search of access. No luck.
If I can remove the headboard cushions, which are somehow attached to the fiberglass inner liner, I will either have access or will be able to create access, behind the cushions.
the cushions must, somehow, be removable, for future reupholstery.