I'll take a stab at this one...

You have likely got a rock or stick down in the blower motor assembly, the bang was probably the debris making contact with the squire cage on the fan motor. You now have a fan that is out of balance or damaged is such a way that it’s making noise. Not that uncommon for people that live where a lot of tree leaves and branches may accumulate around the hood near the windshield.

To test my theory see if you can pull the fuse for just the blower and turn on the a/c and see if the noise if gone. I don’t have my X5 today so I can’t run out and see if that’s even possible. Anyway it’s about 180.00 for the part and about 2 hours to install if you have not done one before.

That’s my guess.