[Otto]

Hi toecheese,

If it were me, I'd probably try to recreate the problem with REW. See if it will happen with pink noise or tones or a sweep at a low volume. I would probably prefer tones, but a sweep will give you an idea of what tone might cause the problem, and pink noise will cast the widest net. Start turning it up (within reason, of course) until you hear it. If you can, good. Now try to figure out what's rattling!

Also, presuming that it could be a driver, you could disconnect one driver, and then the other, to see if the problem follows one.

Good luck!