Engine knock

[Freakinoldguy]

Hi folks,

I own a 2011 GMC Sierra with the 4.8 litre engine. Lately i've noticed a knocking sound comming from the engine when it's cold and I engage the automatic transmission. This sound lasts till I back out of my carport and then it[s gone and doesn't return until the next morning when I go to start the truck again.

I know about the history of GM's piston slap from my misfortune of having owned a 1988 Barretta back in the day but since the knocking isn't noticable till I engage the transmission I wonder if it's piston slap at all.

I somehow don't think a truck with 8000 kilometers should be making these kinds of noises and was hoping someone would have some information about this before I take it into the dealer and make an ass of myself.

Thanks in advance

F.O.G.

 

[kwbudaman]

that could be something as simple as loose bolts on the flex plate to torque converter connection. had that happen.

 

[happy 2011]

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that could be something as simple as loose bolts on the flex plate to torque converter connection. had that happen.


wow losse bolts ponly making noise in am for a min or so. That would be a frist.

Freakinoldguy So does it make the same sound when you put it in drive? I would take it back to the dealer

 

[Freakinoldguy]

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that could be something as simple as loose bolts on the flex plate to torque converter connection. had that happen.


wow losse bolts ponly making noise in am for a min or so. That would be a frist.

Freakinoldguy So does it make the same sound when you put it in drive? I would take it back to the dealer

It only makes the knocking noise after it's sat for a few days and only makes the noise when the transmission is engaged although I haven't tried drive yet, but i will and let you know.

I thought about piston slap but it sounds more like a bearing noise than piston slap and like I said before I had an old 88 baretta with piston slap so bad your teeth would ache till it got warmed up so I'm pretty sure it's not that.

I'm goona take it in for an oil change in a month or so and I'll get them to check it out then but i'm concerned that once it's warmed up it takes a couple of days of sitting before the noise comes back.

Although I left the truck sit for a couple of days and then took a tape recorder out and placed it in the engine compartment before I started it so I could record the sound but no luck................it didn't do it that day.........of course.

Just as an aside my Catatlytic converter makes knocking/clicking sounds when I stop the truck after running it for awhile. I wonder if that's got anything to do with the noise?

Maybe it's a good thing I've still got 6 years on my warranty since finding the issue may take awhile. LOL