Rattling Sound Inside Phone When Vibrating!?

Hello,

I recently noticed about 2 weeks ago, when my iphone 12 pro would vibrate, there would be a sort of 'rattling' sound. I always have my phone on vibrate so I knew immediately it sounded different one day. I took it into Apple because they thought it might be some loose screw so they opened it up and tightened them. However the rattling persists. It seems to be coming from the bottom of the phone, close to the charging port. Could it just be that the haptic engine is faulty and has an issue?

You can even give the phone a very small shake from side to side and hear something inside loose.

I've read some people think it's the camera, but i've had the phone since its release and it never made the sounds previously.

Any thoughts?

Thanks!