Roger,
I like the part about muffling the victim as he's being pounded to death!

As far as the seatbelts go, I suppose scrubbing them by hand in a bucket of tide would clean them. My wife has this nifty rack that fits inside our dryer for tennis shoes... You could lay the belts out on that rack and they would dry with no noise at all. Worse case, hang them in the hangar or in your home until they're dry.
Personally, on the ambulance, I really didn't care about the noise, as we threw the straps in the machine, grabbed a replacement set, and headed off either to post or to the next holding call...