Need help diagnosing a fluttering noise on acceleration

[bjhayes]

I've started hearing a 'fluttering' sound on acceleration but only when my engine is cold. After 10 or so minutes of driving the sound is not there anymore. Dealer kept the car overnight but of course everything is normal sounds to them so it's up to me to narrow down the culprit and I need some suggestions.

The best way I can describe it is a muffled sound of a card in a bike spoke (very different from a tick). Noticeable in the cabin if the radio is turned down. Very noticeable as I drive by walls, other cars and it bounces off.

I first noticed it within a week or so after dealer replaced my leaking oil pan gasket. Maybe coincidence but also wondering if the oil pan removal procedure has anything where they unbolt any part of the exhaust? Possible exhaust leak?

Oil life and levels are good.
Car is a 2009.1 w/ 64k miles, is my daily driver, and is all stock except for the Rotofab intake.
I do not notice any difference in how it drives.. seems to have same power, response, etc...

Any ideas?

I am the original owner and still have till Feb 2015 on my GMPP extended warranty so any input I can get to narrow this down to something that should be covered and I can get the dealer to recognize is much appreciated. Even if it turns out to be something not covered I'm fine with that too just need to get this taken care of.

[Chewy]

Probably piston slap. It's common with the L76 and only happens when cold.

[bjhayes]

Probably piston slap. It's common with the L76 and only happens when cold.

hmmm.. Could be.. but I've never noticed it before and I quickly notice any difference in sound or feel with my car. If it is piston slap why would it all of a sudden start doing this after 5 years.

[Chewy]

Time doesn't have as much to do with it as use. My GT did it, but it went away pretty quickly. I'm not saying that's it, but it sounds like what you're experiencing. It could be that it's just getting worse and more noticeable.

Chris

[I12XLR8]

Is piston slap ever covered under warranty? I'm bringing mine in for what I think is a slap problem as well


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[bjhayes]

Ok... This morning I only noticed it when in gear. In neutral or park I can not hear it... But put it in drive and start accelerating I can. I found a post on a a GMC truck board that describes exactly what I'm experiencing but no one there has responded yet and I'm going to watch that thread too. (http://www.silveradosierra.com/uncat...n-t222722.html).

This all started after the oil pan gasket was replaced. I'm wondering what is involved in that procedure to possibly cause this. Exhaust leak? Motor mount?

[bjhayes]

Ok... This morning I only noticed it when in gear. In neutral or park I can not hear it... But put it in drive and start accelerating I can. I found a post on a a GMC truck board that describes exactly what I'm experiencing but no one there has responded yet and I'm going to watch that thread too. (http://www.silveradosierra.com/uncat...n-t222722.html).

This all started after the oil pan gasket was replaced. I'm wondering what is involved in that procedure to possibly cause this. Exhaust leak? Motor mount?

[G8 GT V8]

I wonder if it is something loose in your exhaust and while the engine is under load, in gear, it's torque twisting just enough to have an issue. It would be worth asking the shop if they loosened your exhaust when changing the gasket. Or, if you're mechanically inclined, you could crawl under to see if you find anything loose.

[bjhayes]

I wonder if it is something loose in your exhaust and while the engine is under load, in gear, it's torque twisting just enough to have an issue. It would be worth asking the shop if they loosened your exhaust when changing the gasket. Or, if you're mechanically inclined, you could crawl under to see if you find anything loose.

Shop was GM dealership that replaced the gasket under warranty. They have done work on the car since new and I have not had any real problems with them. When I ask them about the noise afterwards they say they don't hear anything that is not normal.

Does the GM gasket replacement procedure require any unbolting of exhaust?

Being mechanically inclined is not a problem... My biggest problem is having the time to get to it and the limited space I have to work on it.

Went out again today at lunch (cold start with air temp in the low 70s) and was able to confirm I only hear it in gear while accelerating. As I started to hear it I shifted up to neutral and gave some light throttle and sound is not there anymore (or so slight I can't hear it)... then I shifted back to drive and gave some light throttle and there it is again. After 10 or so minutes of driving it's no longer notiecable at all.

It may be piston slap but seems odd it would only be noticeable when in gear under load. Makes me think something in the exhaust leak side... but who knows.

[Chewy]

I only heard the piston slap on my GT when under a load. I always made sure to take it easy until up to running temp.