There is something that happens to E30 M3 OE cats that is truly unerving. The cats as they age begin to loosen up inside and eventually start to rattle in such a way that it feels as though the rattle is right there in the cockpit (no pun) with you. It literally drives one "up the wall".
The rattle is different depending on whether it is cold outside or not. It is more pronounced the colder it gets and can make driving much less of a fun thing than it should be. I have been experiencing just that this winter.
Today I went to a self-serve carwash and gave the car a bath. She looked great after the wash and I drove off afterwards and did not notice the steep incline of the exit. It was s t e e p
!!! Needless to say, I bottomed out.
So as any loving owner would... I also freaked out. What have I done? I have destroyed a cross member or even worse an area of the flat underside of the car... or worse yet... some pivotal chassis part. Aaaaaargh !!!
After I was finished with a litany of self-insults I went to a garage nearby and asked them to put it up on the lift. I looked at the underside and much to my surprise... I had dented the front cat square in the middle. Also, I had been so upset that I had not noticed that the rattling noise had disappeared.
So my cat noise is "fixed" (for now) with an inadvertent accident at the wash.
How cool is that?
PS... I'm replacing the entire center section (new cats) in March...