Don't know anything about the Silent Rider but here is my experience. Got my 825i in April of '12, seemed noisy but I thought maybe that's the way all of them are. This spring I noticed with it idling and I was loading something in it, it seemed as if more noise was present in the area in front of the left rear tire than behind the machine where the exhaust outlet was. I kept investigating this and eventually one day when I first started it and everything was cool I immediately placed my hand over the exhaust outlet. (if you burn your hand trying this I'm not responsible) I could hold my hand and it never did build up any resistance. This suggested that I had a leak somewhere else. I "unfolded" the two stainless steel retainer bands on the exhaust shroud over the tailpipe and removed it. In the area mentioned near the left rear tire there is a coupling that slips together the pipe coming from the engine and the muffler. Mine was slid apart for some reason and the exhaust had been blowing out there since new. I talked to the dealer about this and that's a whole other story. "Yeah, never heard of that before, bring it down and leave it and we'll try to look at it, we're running about 3 weeks behind so I hope you don't need it." I went home and went to work on it myself. Everything was bolted up and looked like it was supposed to but it just didn't come together at the joint. I took a 2x4 and did a littler persuading on the front end of the pipe where it makes the bend off the manifold and just a little tweaking there and the joint slid together at the muffler. There is no comparison now with the sound level prior to this. I encourage you to be very easy if you try the persuading like I mentioned because I'm sure something real expensive could get broke if too much force is applied.
Good luck and hope this helps.
Mike