engine noise

[cmd]

2003 h2, i have noticed a rattle coming from the motor at low rpm, In Park position if i bring up the rpms and let go of the gas you can hear a rattle as the rpms fall between 2000 and 1000 rpm, the same noise under load. Not sure if it is from the top end or bottom end of the motor? .Any one have any experience with this ?. cant determine if it is the valves or what.

Thanks

[intimidator]

it's called piston slap due to the fact that gm went to a piston with a shorter skirt.
when carbon builds up on the top of the piston it causes the piston to rock in the cylinder and cause this noise.it usually is more noticable cold than hot and causes no damage . do a search for gm and piston slap

[cmd]

I read up on it a bit, does this get worse over time, is there any thing you can do to clean up the carbon deposits or reduce the noise?. what year is your h2, did GM make changes on any newer models?

Thanks

[Yetti]

you can try some GM top engine cleaner. it can be poured into the air inlet on the intake under power and it will clean out the carbon in and around the pistons. I would recomend letting the dealer do it if you think its a carbon issue. that way if they do something wrong they will have to deal with it.

[f5fstop]

Not sure if it is piston slap, since you seem to imply it is happening all the time and piston slap usually disapears as the piston heats and expands and fits the cylinder.
It could be a dirty top engine that someone menetioned; so here is a good cleaning procedure, short of removing the heads.

Option 1.
Remove the spark plugs, pour in some GM top engine cleaner or Chevron Techron, insert plugs FINGER TIGHT, let it sit over night DO NOT START ENGINE.
Next day, REMOVE PLUGS, crank over engine a few times to clear liquid out of cylinders. Install plugs, and start the engine.

Option 2
Purchase a few cans of GM top engine cleaner or Chevron Techron and run it through the fuel system for a few consecutive fill ups.

Option 3
Both 1 and 2.

Would love to see you purchase GM top engine cleaner it helps my company; however, to be honest, its main ingredient is Techron by Chevron. Just make sure to get the high concentration of Techron containers at a good auto store.

Now, how is your A/C operation?
Slugging of the A/C lines can also cause a sound like a rattle, usually heard under heavy acceleration, but can sometime happen under an idle condition.

Can you recognize the area it is actually coming from with the hood open?

[cmd]

this occurs with the ac on or off. I cant determine if it is from the bottom or top end, i am leaning more towards the bottom end. I have a appointment at the dealer next week to have a few things checked, I am out of warranty of course, anything you could recomend me bringing to their attention that would be a known issue perhaps. the dealer is quite a ways out for me and i would rather be a bit educated before going out

Thanks for your help.