I'm having a similar problem with my 02 525i - I have Continental ContiExtremes and it seems like they go out of balance as soon as I get them balanced - all 4 tires!!!. BMW gave me a speech about how the tires are "cupped" and thats probably whats causing them to continuously go out of balance and will need to replace all 4 tires. The tires are only a few months old and I'm hesitant to just dump them but that looks like its what its going to have to be.