I had my muffler fall off a while back, the exhaust ended right behind the cab so it was straight out of the cat. It didn't sound terrible bad, but the drone at highway speed really got to a guy after a while. I ended up just putting a magnaflow wanabe on it and it runs fine, no rumbly, but it doesn't drive ya crazy on the highway. I'd prolly go with most of the suggestions here to put a good full flow muffler on