Over the past week i have noticed or at least started to really notice it I guess maybe because it's window down weather?

When driving when the vehicle is in motion, ONLY when I am near something that can echo/exacerbate noises and make them louder do I hear a hissing sound like air being let out a tire until the truck comes to a stop, I don't recall ever hearing this noise really, and am wondering if I may have some kind of vacuum leak in the rear end?

At first I thought it was happening when my foot was on the gas and it was from the engine bay, but started to realize even with my foot off the gas and coming to a stop I hear the noise.

It only seems to happen when in motion, i've climbed under the truck and cannot hear it when sitting idle.

What could this be? Or is it totally something not even to worry about lol?

My brakes work, my ABS works I believe, my differential oil is full, no lights on dash. Just curious on your opinions?

 

No vacuum anything back there. There is the vapor canister somewhere, depends on what year truck you have. (and you really should put that info in your sig, and profile.....)

Not just tires-on-road noise is it?

 

Lol never thought it could just be tire on road noise, can they make a hissing sound? And I have a 2000 Dodge RAM 1500 Laramie SLT, RWD 5.2L V8 Magnum.

 

Depends on the tread pattern. If they are street oriented tires, then yeah, good chance.

If you step on the brake lightly, does the sound change?

 

Not from what I can tell, it just completely stops when my tires stop rotating lol, I don't recall ever hearing the sound that bad especially like in a drive thru, thats when I first noticed the sound lol, hadn't heard it before as noticeable I do believe.

And like I said before, giving it gas in Neutral or Park, I hear nothing from the engine bay, nor under the truck.

 

Check fluid level in the rear diff, and tire pressures. Make sure everything is good there.

Haven't changed tires of late have you?

 

Fuel pump, rear breaks, differential, etc.

 

It may be my rear drum back plate scraping the drum when i'm driving, it seems like this guy with a Dodge Dakota had a similar issue where he could hear it when you were near things that echoed sounds:
How hard is it to bend the backing plate a little if it is bent? Or would I need to replace it.

 

They aren't real thick. Could probably bend it with a small pry bar.

 

they don't usually get bent though.
put the rear end up on jack stands and have a driver operate it while you very CAREFULLY listen. beware of moving tires, drive shafts, etc, they will kill you.