Popping Sound after I shut off the car.

Jimmy_the_Greek · February 12th, 2004, 10:20

My car makes some interesting noises at idle and especially when I shut the car off. At idle, there is a humming noise and when I shut the car off, the noise continues for a second (almost like a squeak). It sounds like a pump or something that is struggling to do its job. Immediately following this, there is a popping noise (that actually sounds similar to the noise that the trunk makes when you pop the trunk).

Back at 38,000 miles, I had a fuel filter go bad on me and I tried to make it home about 4 times and it kept dying on me. I got it towed to the dealer, they did the 40K service, and that solved the problem. I only mention that because it may have something to do with the noises. That is literally the only problem I have ever had with the car. The car has 61K on it now and VW just did the timing belt at 56K.

I have also noticed that the engine noise has gotten louder in general since I first bought the car and I was wondering if this was normal or if it could be indicative of a problem. As far as I know, the exhaust system is in perfect condition. The car has been in for every scheduled maintenance visit and I have been using Mobil Delvac since I bought the car with 18K on it. I have also used the VW recommended Stanadyne fuel conditioner since Fall '03. Anyway, any advice or ideas would be greatly appreciated.

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McBrew · February 12th, 2004, 10:43

Maybe the anti-shudder valve getting sticky? Here's a pic of my anti-shudder valve. The rod that my finger is touching... you should be able to push this about 3/4 inch, and when you let off, it should spring back. Do this with the car off. The only time this valve moves is when you turn the var off. The valve closes (rod moves in), then a few seconds later (after the engine has stopped running) the rod moves back out.

If the rod sticks in the closed (in) position, the car will not start next time you get in. It will crank and crank, but never start. If that happens, you can manually pull it back out. Gunk from the EGR and PCV clog up the mechanism.

EDIT: I don't know if this could cause noise at idle... but it could cause noise when shutting down.

Jimmy_the_Greek · February 12th, 2004, 10:54

Thanks for the advice, I will check that out and get back to you.

weedeater · February 12th, 2004, 10:59

Don't know about the 'hum', but the thunk after shutdown is the anti-shudder valve. It's normal. To me, it sounds like someone closing a car door nearby.

Jimmy_the_Greek · February 12th, 2004, 11:05

The anti-shudder valve does spring back and is not sticking. However, I can see why it would make that noise, with that little arm thumping the housing. Now if I could just figure out what that humming noise is...

McBrew · February 13th, 2004, 13:08

Vacuum leak somewhere? Maybe if you leave the hood up while it's running... have someone else turn the key off, you might be able to pinpoint the source. Good luck!

mgwerks · February 13th, 2004, 13:24

You know, it kinda sounds like the old vacuum leak noises from air conditioner doors, headlight doors and the like. I vote for a vacuum diaphragm somewhere. Try using a stethoscope as an assistant turns the car off multiple times to pinpoint the source of the noise.

SoCalJames · February 13th, 2004, 13:32

Perhaps the humming noise is you HVAC fan? Perhaps it's the cooling fan? I don't know under what conditions (if not all) these phenomena occur. When I lived in Michigan, fan speed 1 would moan in very cold weather, even for a moment after turning off. Re; the popping noise- It probably is the anti-shudder valve, mine does this as well.

J