Sudden, temporary hissing noise
 

I recently bought a 1999 Blazer. I've had the following work done: new radiator hoses, replaced one idler arm, new Bilstein shocks, new rear brakes and rotors, new intake gasket. It's running and riding pretty good.

A couple days ago, I was driving up my friends driveway with the windows down, and suddenly there was a loud hissing noise. I thought I had punctured my tire, or that my shock had busted (but I thought, shocks don't have air). It sounded kind of like the sound that comes from an air compressor when you pull the release valve. The sound lasted about 10-15 seconds and stopped.

At the exact same time, there was a loud scraping coming from the rear brake. The brake scraping continued as I drove on up to my friends house. I thought something on the brake had broken loose. Anyway, when I left, the scraping from the brake lasted about halfway down the driveway and then stopped. I haven't heard either sound since.

Any ideas? The Blazer seems to be running fine. Everything seems to be working.

Thanks in advance for any input.

most shocks on the market now adays are nitrogen or such charged so don't rule out a shock blowing just yet :icon_steer:

I took a good look at the shocks after work today, specifically the front passenger shock. I don't see anything noticeable or out of the ordinary, no leaking oil, no cracks, or fractures. The shock seems normal. So, I really have no idea what the hissing was.

Well the only things that comes to mind that would make the noise you described would be either a shock loosing charge or maybe the AC unit with a sudden leak.

The rear brake growling at the same time could be just luck but almost leads me to a rear gas charged shock popping a pin hole and blowing nitrogen and maybe temp. freezing up a brake or line. but if the sound lasted 10 to 15 seconds a shock prob wouldn't have lasted that long. :icon_gunhead:

Thanks odat. How would I figure out if a shock had lost charge? (The AC seems to be working fine.)

Well you could pull the shocks loose and see if they extend on their own. But they can be sometimes be a royal PIA to get collapsed back into position.

Over the years I have had new heavy duty charged shocks delivered to the shop that have had the nylon straps either broken or dislodged and to install them I have had too install the top mount and use a floor jack under them to collapse them up enough to install the bottom mount

Rusted dust sheild hitting rotor?
Dorman - OE Solutions Brake Dust Shield Pair 924-222: Advance Auto Parts

So, if I took the shock off, it should extend by itself, otherwise it's blown?

good shock = sshock extends by itself
bad shock = shock stays in place

yup - a good gas charged shock should extend itself