Upgraded to 214 Rims Problems / Questions

[jgmsethi]

I recently purchased a set of 214 rims off an x6 for my x5.

Brand new tires Continental Run Flats.
I had them mounted balanced etc. Had to bore out the center .1mm for the rears to get em to fit.

These are the first pair of 20's I have ever owned on any car.
The drive is smooth etc until I hit a bump then I hear a low rattling sound off the back.

First I thought it was my plate but thats secure now and I still hear it. Its getting very annoying.

Also I heard that the MPH reading will be wrong on my speedometer. Anyone else have this issue?

I love the rims but the noise is getting to me any one?