You said louder as you go faster, but does it change with shifts?

I had this with mine, but it was because I removed the ABS sensor. Upon reinstall it shifted too far forward and was riding on the pick-up ring! Glad I drove it just around the block. Thought it was the bearings since it was consistent with speed.

Usually if bearing are making the noise it will go away as you turn one direction and get louder turning the other way. Although driving with bad bearings is... well bad.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car