Thread: Raspy hiss from dash/center-console when Accelerating

Hi All,

I'm brand new to the forums and have done a little searching without luck (I didn't try too hard.)

I have a 2008 grand prix with almost 80k miles and no mods. Under hard acceleration I'm getting a raspy hissing noise that follows the RPMs of the engine. It seems to be coming from behind the a/c control area (in the dash somewhere) or the front portion of the center console. When the engine is cool, the noise is more of a raspy squawk/squeal. It is louder when the car is not warmed up and gradually changes to a quite raspy hiss at the car warms up. It verges on barely audible once the car is warm, like when I swung by the dealer (who told me not to worry about it .

The car is running smoothly with no dummy lights and the tranny is shifting as smooth as I ever remember. I haven't noticed any power loss, just the unusual noise.

It makes the noise with AND without the A/C fan on.

Any help or ideas would be appreciated!

Originally Posted by scottydoggs

could be a broken vac line to the vent direction diaphragm. you should have 2 of them on on each side of the dash center console area.

does your defrost, vent, and floor vents all change and operate like they are supposed too?

I believe they are all working fine. I will double check that they are all working properly.

Can I visually check for leaks or damage without taking the dash apart? How would I go about checking?

Thanks for your help!

I'm going to take some things apart this weekend and see what I can find. Where in the pictures are the diaphrams and how would I check them, any ideas?

The issue is more common now but I only notice it when I punch it on the highway. Through some other browsing I thought it may have been air in my cooling system since I've heard the glug-glug-glug watery noise behind my dash in the past. I bled the system as instructed and found no improvement to the current noise I'm having.

Does anyone have other ideas on my issue? Any chance it could be belt squeel, or an exhaust leak? My gut feeling is it's related to fluid or air flow.

Thanks gents.

Scotty,

Before I had read your post I read a couple other places that I could bleed air from the heater core (and the whole system) if everything was warmed up and the heat blasting on high by simply bleeding from the bleeder screw.

I did this and it seemed much hotter the next day. Then a few days later it doesn't seem quite as hot anymore. Can I successfully remove all the air with my method OR is your's a better approach?

In your description you said remove the hoses from the alt, you mean alternator? I wouldn't think coolant lines would run to that but I'm new to this. So "flushing" with the garden hose does what - forces air out of the heater core and then with lines refilled the system should be air free?

Thanks for your help.

Scotty, I see what you are talking about with the hoses and heater core. My first concern is now that I am in MN winter, would I be at risk of freezing my block by replacing the amount of coolant in the heater core and attached hoses with pure water vs 50/50 mix?

Second, when you say "flush, refill hoses, and get back on engine quickly" are you just getting the fact that, after flushing the heater core, I don't want to let water drain out of the hoses because it will just cause more air to get back in the system?

Thanks man.

Would it maybe be worth paying someone to flush the system? Would they for sure get all the air/crud out and then I would have good coolant for sure?

I'm leaning that way.

I put in a new thermostat and bled from the bleeder screw again and things seem to be working well now - once temps reach sub 0degF it may be another story. I still think a system flush is in order once spring rolls around.

How much waste fluid will I end up having for your flushing procedure listed above. A couple gallons or like 20 gallons? Thanks.

If I do a system flush, that fluid coming out of the upper hose has to go somewhere. Just curious how many buckets to have to catch all the old coolant and contaminated water.

I also have an 08 GP base and had this same issue with the hissing sound. I thought it was a pulley for the longest time cuz it make noise parallel with RPMs around 3,000 and up.

Anyway, I developed a heater core leak and replaced that and (knock on wood) I don't hear the noise anymore. Noticed the hissing sound around 120,000 mi. and heater core gave out around 128,000 mi.

This was all very strange to me because prior to all both of these issues occurring, I did my normal scheduled maintenance coolant flush (prestone and 2x w/ distilled) and then 3 months after the flush I ended up replacing the tensioner - added more new coolant, and then 2-3 months after that I replaced the water pump (thought it was the hissing - not the case), so put in more new coolant. So this coolant system had been getting a lot of attention and wasn't neglected at all. And I always bleed and use the Lisle spill free funnel to burp the system.

I'm about 4-5 days into my new heater core and I don't hear the noise anymore (again...knock on wood), so only time will tell.

I'm guessing I might have had a slight blockage and the hissing noise was faster moving coolant liquid rushing past the blockage upon acceleration. Because obviously the water pump rotates faster when you accelerate so fluid moves quicker. Again, I just don't know for sure, cuz my heat always worked great and my coolant is bright orange from regular servicing, so my instinct tells me a blockage was highly unlikely.

But the noise seemed really sporadic to begin with. Some days it was clock work - 3,000 RMPs and higher on every acceleration. Other days it was faint and I couldn't hear it until 4,000 RMPs (obviously a hard acceleration). I even bought a engine stethoscope and was listening to different pulleys because I thought, for sure, it was a pulley.

I think I cracked my heater core because I had AC running to both upper and lower vents, let me explain. Normally, I just run AC to upper vents on a daily basis in summer. I went on a 6 hour road trip, so for the sake of comfort, I had AC running to both the whole time. Well my GP (idk about everybody else's) doesn't not have a Heater Control Valve, so AC is always flowing through the Heater Core even in the summer. A heater control valve will allow the cooling system to bypass the HC when car heat is not needed (aka summer). But for in my case, if the AC is on, air is never blown over this HC (to produce warm air), so you never know the difference, although the floor air vents passes right next to the HC cover. So I speculate that the constant cold air next to my HC for such a long period of time gave it a stress fracture. If you've never seen a stress fracture, put boiling water in a glass cup, pour it out and then put in cold water, it will crack the cup in half.
Or maybe I'm over analyzing it and the HC was just old and started leaking.

Anyway, there's a really nice thread on here for heater cores I used: http://www.grandprixforums.net/threa...61#post1444261
It wasn't the most difficult job, more so challenging because of the location. I definitely wouldn't want to do it again, my back hurt for a few days.