2000 Blazer 4X4 2 dr. 110,000 mi.

I get this noise/sensation that sounds like a short burst of pressure being released. it happens when the truck has been sitting for a while, engine off. I start the truck, wait for the idle to regulate (more common in cold temps), put in gear (either reverse or drive), and without applying the gas, I let the idle take me out a few feet. After about three or four seconds of roll, a noise/sensation that seems like released pressure comes from somewhere in the engine compartment, or possibly the front end steering/suspension. it's like opening a new 2 liter of soda, but not as high pitched.

My usual mechanic hasn't experience this with my truck yet, but when i described it, he never heard of anything like it. anybody have any clues? shocks? break line? steering? something in the engine compartment? weird stuff.

 

ABS brakes makes a wierd noise on mine when backing up.. not a pressure sound though..

 

yeah, it's kind of like the front end was holding a deep breath and decided to exhale. i don't know how else to describe it. my mechanic replaced my wheel bearing this morning - he forgot to listen for the described sound when he moved the truck to the garage, so it's still a mystery. but... he mentioned he did something with my abs, however the truck still makes that sound.

 

Is your foot at all on the brake pedal when this noise occurs? I have seen brake power boosters leak vacuum, and can have that kind of noise..

 

Sometimes my foot is just touching the brake pedal, but not pressing it down. I'll release the pedal after shifting in to gear, then always wait for the release. it will happen 100% of the time when the truck is ice cold. if i stop at a store, run in and out and move again, the odds of it happening are 50/50.

The sound does seem to come from the area around the pedal.

 

Just to hazard a guess, from the symptoms you describe, I would think it was the ABS system initializing..... I think. They still do that, don't they? Back in the day..... customers would always complain about the rude noises they heard when they first started the car moving.