I recently did the famous "golf tee mod" on my 2012 128i. The engine is completely stock. I used a zip tie, and completed it in under 5 minutes! The sound to me is only really noticeable when driving and RPMs are below 3k. I would really recommend this mod to anybody in a 1 series looking for a little bit more sound from their exhaust!
Here is a before and after I recorded:
