If even the slightest bit of pressure is placed on the case directly above the disc drive as it’s running, there’s a metallic “vibrating” noise.
I actually had to loosen the screws on the case to stop it doing it all the time after reassembling it. I thought perhaps I’d tightened the two halves of the shell together too much.
Also, is the read/boot time “normal” between inserting a disc and the black Xbox splash screen showing?
Video here: