As written here: http://www.xoutpost.com/bmw-sav-foru...on-broken.html

I had that "rrrrrrrrrrrrrrrr" at exactly 1400 and 1900 rpm when accelerating in D mode. Had that now since about 3 months and it was getting worse.
Dealer did a test drive and the first reaction was: new transmission. I told them that this is not an option since I believe only the lock up clutch might be the culprit.
They changed the transmission oil now (at least half of it - they said they cannot change the oil which is in the TC ....?!?)
I was also told that the error "gear monitoring 4+5" (?? Gangüberwachung 4 and 5) had been stored and after a 60 km test drive with the new oil it did not come up again. Now the rattling is much better but it has not disappeared.

Not really sure what to do now because a tranny change would be about €3.500.- (material only).

On different webpages I could read that changing oil more often might help here but ........ ?

Helmuth