Why do my bullets make this weird noise?

[Gonzo Z71]

why do they make a sucking/vaccuum like noise when i run the truck a little? it doesnt make that noise when i start it up. Is there a way i can get rid of that noise its starting to bother me and im just thinking to cut off my bullets and put back on my flowmaster. i have a 97 Z71 true duals no x-pipe and its a chevy 350. Thanks

[GarnerZ]

i had true duals bullet and they did the same thing, i posted up a while ago about it. ended up going back to flows

its like a fluff fluff noise right? its just they way they are made sounds horrible at idle on a stock motor

[4mcrue]

It's just the way a louder type straight thru muffler sounds on a newer truck, my cherrybomb's do the same thing. I just ignore it.

[Gonzo Z71]

well im glad im not the only one who has had this problem. Is there anyway i can make this noise go away? i dont want to cut off my bullets.