New exhaust hissing sound?

[JPB]

I had a muffler shop replace my stock muffler ('06 1500) with a 40 series Flowmaster, single in dual out a little over a week ago. The other night I noticed when I would hit the gas from idle there was a short hissing sound, which sounded like it was coming from the exhaust. I had been driving around town running errands for several hours when it started making the noise. The sound went away the next day and hasn't come back. Does this have anything to do with the pipes being heated up from so much driving, or does it sound like something else?

[mmmikkke]

I wonder if some "label" on the inside of the muffler was curling back, making the hissing sound, and then after it sat overnight, it was completely charred and toasted. So now it's gone.

 

That's my guess and I'm sticking to it.

[Raptor660r]

My guess its a seal problem. It might be a crack in the weld. Get under the truck, and look for black soot on the pipes around the welds, and seal areas.

[JPB]

The sound came back. It doesn't do it until the truck is warmed up. Anyways, I took my truck back to the muffler shop to have them look at it. The tech double checked everything and said there were no leaks and all looked fine. He did say he could hear the sound, and that it's from back pressure being built up. He said since the air filter is paper that it's trying to suck in more air than it can, which creates the brief hissing sound. His logic was that the exhaust was getting the air out faster than the air filter to bring it in, hence the purpose people add in intake or cotton filter. Does this sound right?

[JPB]

Nevermind. After some more driving around, it appears the sound isn't coming from the exhaust. I think it has something to do with the suspension. A little while ago, I was getting into the truck, and it make a creaking sound (the same hissing sound I was hearing). It makes the creaking sound as I said before, when I hit the gas from an idle, but I don't know what's causing it.