Finally got a CRX HF, trying to restore it. Last issue I have is when I accelerate "hard" there is a metal ringing noise coming from the axel back/hatch area from the car. I've inspected it myself like 20 times, couldnt find anything loose, already took off all heat shields, including the one from the engine bay. Car doesn't have catalytic convertor, replaced all bolts/hangers/ b pipe, header, etc, promise nothing is loose but still have that metal clang when I accelerate. So annoying, has been like this since I bought the car.

Any ideas what it could be? I took it to 2 muffler shops and they said there wasn't a leak, none in the header area or the axel back. I thought axle back, but when I shake it around, theres nothing loose in there. So confusing. I took apart all trim in the rear cargo hatch area/made sure nothing was loose on the inside of the car, and still does the metal ringing when I accelerate

If I don't accelerate hard/barely tap the pedal, there is no noise. Anyone got ideas? Last option is just replace axle back, but that might not even be the issue / would cost money