I have had an exhaust rattle for a while, and been unable to figure it out. Its loud as hell, and doesnt take much of a bump at all to make it do it. Yet when i I shake the tailpipe or midpipe...nothing, its solid. I have heard that when the cats go on a 528i it can sound like loose marbles bouncing around, I believe this is my problem, and its friggin annoying.
Now to my question. Does this sound right? If so what are my options, cheapest cats, "nonbmw" cats, or can I hollow them out (done it before but will this set off a check engine light or somthing else). Basically what is the cheapest way to make this rattle go away?
Any tips are much appreciated.