Mystery Noise
 

As I was going to pick up last minute items to replace my hub, this noise started up:
I put my code scanner on but it says that everything is fine, I can drive the car but choose not to until I can resolve this. It also makes the car idle a bit rougher than normal. Does anyone know where this sound is coming from and what it is I need to do to correct it? Driving my brother's Aztec is killing me on gas!!! Thanks

im not sayin it is this but the only time i heard something similar was a alternator going bad

probably a bearing someplace- you need to pinpoint it. Could be alt, idler pulley, or even just a vacuum leak.

Idler pulley

When was the last time the water pump was replaced? Might wanna try wiggling the water pump pulley to see if there's any play.

Well now here's the thing. When the engine is cold it sounds fine and doesn't make itself known until I drive down the road a bit and when I turn the car off it sounds like something is depressurizing, sort of like a woosh of air or something. I tried to look and see if it was any of the vacuum hoses but they look fine on the front of the engine but I will have to take the intakes off to check the hoses that run under them. Is there a way to test if it's the idler pulley? Well I imagine take the belt off and check it, which would be a good time to change the belts anyway...

Haven't done anything with the water pump at all in the almost four years that I have had it. I will check the idler and water pump tomorrow since as I said will finally give me a reason to change those belts. Thanks for the input guys, I appreciate it. I gotta keep the Obsidian ti on the road!

Can you isolate the noise to the back, front or either side of the engine? Does it fluctuate with engine rpm? Now that you mentioned the "depressurizing/wooshing sound", I'm thinking you might have a bad CCV (crank case vent valve) or a bad secondary air pump check valve orrrrrr a leaking secondary air pump. Here's how you could check each one of those things:

CCV VALVE - It's a black disc shaped plastic piece located towards the back of the engine up high, just to the left of the upper intake manifold. It should have a little slit on the bottom of it. With the engine running, place your finger over the slit on the bottom of the CCV valve, if you hear the whistle note change, your CCV is clogged. Unfortunately these things get brittle over time, so if you try to take it apart and clean it, it'll likely crumble in your hands. The part costs between 50-60 bucks new.

SECONDARY AIR PUMP - This is a black pancake shaped plastic valve located just aft of the airbox. There's two hoses going to it. One goes to the airbox, the other is a rigid plastic line that goes across the front of the engine compartment to the secondary air check valve. The secondary air pump is composed of a stack of disc-shaped plates that are held together with 6 aluminum rivets. Over time, these rivets break and allow the plates to separate which in turn allows the pump to leak. The pump ONLY RUNS FOR THE FIRST 30 SECONDS after a cold startup. So to check it, wait until morning or after the car has been sitting for several hours. Pop the hood and be ready to run around and stick your hand near the secondary air pump IMMEDIATELY after starting the engine. You should hear the pump running. If you feel air blowing on your hand, your pump is probably leaking. You can easily fix it by removing the pump assembly and replacing the broken rivets with nuts/bolts.

SECONDARY AIR PUMP CHECK VALVE - this is a black disc-shaped plastic piece located on the front passenger's side of the engine compartment just aft of the radiator fan. It'll have a rigid plastic hose going from it across the engine compartment to the secondary air pump. This valve should only allow air to travel in one direction, from the secondary air pump into the exhaust stream. With the engine warm, but not running, squeeze the two tabs on one end of the plastic hose and pull it off either the check valve or the secondary air pump. If you disconnect it @ the valve, make sure the hose is secured so it won't get tangled in the belts or fan. If you disconnect it @ the pump, take the same precaution as to not let it get tangled in the belts or fan. Start the engine, then feel if air is being pushed back through the plastic hose or the check valve itself. You shouldn't feel any air at all and if you do it may be hot so be careful. If you do feel air, your check valve is bad.

INTAKE BOOT - You should also check your intake boot for cracks, they're known to split at the seams and it's usually invisible to the naked eye. The best way to check it is to buy a can of brake/parts cleaner(NOT CARB CLEANER). With the engine running, spray a sh!tload of brake cleaner on the intake boot. Try to get it up underneath the boot as well. This is the ribbed rubber boot, just aft of the MAF sensor and airbox. While you're spraying brake cleaner on the boot, listen to the engine rpm's. If you hear it fluctuate, usually it'll rev up really high, then you need to replace your intake boot asap. You can temporarily fix it with duct tape. Just wrap the heck out of it to create an airtight seal. Note; you should also spray brake cleaner on any vacuum hoses as well as around the upper and lower intake manifold especially where they connect and mount to the cylinder head. Same thing, if the rpms rev up, you know you have a leak.

WATER PUMP BEARING - Grab the water pump pulley and try to wiggle it. you shouldn't have ANY play whatsoever.

Hope this helps, best of luck!

Does the sound stay constant with fluctuation in RPM's, or does it get higher pitched or louder as RPM's increase?

IIRC, the sound is constant but at speed it's hard to tell since the engine and road noise drowns it out, but once I start slowing down it still sounds constant.

Thanks, I will print this out and check them tomorrow. I just replaced that rigid plastic hose a while back, I am more than a little familiar with it. As for the air pump, I am definitely going to have to try to fix it because it looks like the PO tried to superglue it shut and a number of the rivets seem to be either broken or close to it. Any idea to what size and length screws to use?

Oh, I almost forgot, the sound is loudest at the front.

if the noise doesnt stop after 5mins of running the car after a cold start you can rule the secondary pump out.. since it only runs 30secs after a cold start.. yeah mine did somewhat a noise like that but it only lasted like 20seconds once a day or twice a day.. after that never.. i did what jess said with nuts/bolts and well is much much quieter now but can still hear it for the same amount of time

Yeah I ruled out the pump since it was only after the car has been running for a while. When the engine is cold I don't hear the noise at all, but after I drive it approximately 2 miles it starts up.

Took a look at the alternator idler pulley and that might be the problem, it might not be. It was kinda of freewheeling kind of loosely in comparison to the A/C idler and there was some bearing noise to it, so I have ordered a new pulley to see if that resolves the problem.

I would think that if it were anything running off of the drive belt, the noise would fluxuate at least a little with an increase/decrease in engine RPM, but perhaps not. You might want to try spraying some belt grip on the drive belt and see if that makes any difference in the pitch or intensity of the noise- I had a bad belt tensioner and a bad pulley and in both instances, the noise coming from either changed slightly once I sprayed the belt, and that's how I was able to isolate the source of the noise. Just a thought.