I've got a fluttering hollow type sound that either sounds like it's coming from under the hood or the exhaust. I have a Kinetix V4 Upper Plenum installed, checked for leaks and couldn't find any but I noticed it's rubbing on the hood, could this be it? Something else that alarmed me though was that I just topped off the coolant and in the last 2-3 days the level has gone down about 1 Inch, could this be related? I'm not seeing any leaking fluid under the car or anything, though I did have it full to the rim what reasons would this have gone down by 1 inch already?

I read on some other forums that it could be a screwed up head gasket or cracked head, is this true? I have an extended warranty 7yr/100k, would this type of deal be covered? (of course i'd put the oem plenum back on before bringing it in). Or could it be an exhaust leak, or something wrong with the cats?

Anyway, it's driving me nuts.. Anyone have any ideas? Also, before I can take it in I need to put the oem plenum back on and need the long bolts, where can I buy these? Also, one last thing to note would be that I think the noise starts to happen more after the car heats up.. Sometimes I won't notice it, then park for a few minutes then start the car up and begin driving again and it'll start, it definitely doesn't do it as much when the car is cold, I feel that there is performance loss too but ONLY after the car heats up. I have a jwt popcharger too but it's not on at this time, I have the stock intake in right now. My exhaust is a Greedy Evo2 catback.

Any tests anyone can suggest to figure this out?

Thanks!

 

A vacuum leak makes a hissing sound. You are sucking air "into" the motor from someplace that you should not be. Sometimes you can feel this with your hand. Covering the area with your hand or towel may alter idle RPM.

An exhaust leak under the car may be deceiving. It may sound like it is coming from inside the engine bay but it is not.

 

David,

Previously I had a leak in the past with the Kinetix upper plenum, I do know the vacuum sound you mention. I was able to feel it with my hand when it was bad and spray (brake cleaner?) around the plenum and it would change the idle. I ended up re-seating the plenum with some gasket sealant and it no longer does this. The sound definitely does not sound like a hissing but more or less a hollow or metallic fluttering/gurgling noise. I've also noticed when going over bumps it will change tone as well. You must be accelerating for it to happen, and it can occur at 2.5k-3.5k or over 5k or 6k under acceleration. Interesting what you mention about the exhaust leak being deceiving, I suspect the guys who installed it to be morons so that may be possible. Is it possible to see cracks or leaks in the Cats by looking under the car with light without having to raise it? Perhaps I could take pictures if needed, also I could do the same with the Plenum and Hood since they're rubbing.

Also, it looks though the coolant level was lower this morning though it could be because of the cold over night. I drove to work and the level was much higher. I'm wondering, is it possible that because I topped off the coolant, later when I drove it the pressure forced it out the top of the resovoir drain and that's why it lowered a bit?

Anyone else have suggestions or anything else I can look for as well?

The car has 70,700mi on it.

Thanks.