I run a LRD Pro 4R Carbon on my YFZ450. It's not too loud and it provides awesome acceleration. LRD has a slip on available for the Can-Am DS450. With the quiet core installed it's at 97db and 100db open.
well...ALL after market exhaust are gunna make you noticed...97db is still pretty damn loud. hell 90 db is loud. almost all the aftermarket pipes have somesort of a quiet core, hmf, motoworks, lrd, lte, fmf, and they all get the dbs about 3-5db lower.
I would try the FMF Q4 I thank it is. but seriously thanks for wanting to keep it quiet!! yes my DS has a SR4 carbon full on it, and its a pretty loud, to loud honestly, but its for the closed track too. I have the stock exhaust on my to 250 Raptor trail beast primarly cause i want to keep it quiet for the woods. I'm sick of seeing the avarge joe out at the local ride spots, with the only mod being just pipe, and they want it just to make it loud, cause they thank its cool. then they sit there in the parking lot and rev the piss out of it, probably sure youve all seen this happen a time or 2. just burns my toast thats how alot parks get closed just ignorence. so once again man, lots of respect thats awsome you want quiet as much as power