My little 300SE has the coolest little exhaust idiosyncracy; it sets off aftermarket car alarms when idling along in parking garages.
It has it's 6th free Midas muffler on the rear, and it's 3rd Ansa center muffler.
It's very, very quiet under all conditions, but has just a little deep tone at idle that the aftermarket alarms don't seem to like. I love it, a super-quiet Benz just cruising along the lot, setting off every alarm in sight.

Most fun I had with it was when I was waiting for the grand-daughter at Mcdonald's, and some punk in a ricer parked next to me, right in the handicap spot. I dropped it in drive and his alarm went crazy. He ran out and beeped it off. As soon as he got back in line, I dropped it in drive again. I smiled all day.

DG