From my research it might be the A/C compressor. I've been using it a lot lately. Just a second ago I started the car again. I didn't use air conditioning yesterday and I did not hear the noise. I'll have to test it out for a few more days. Does anyone know if the A/C has to be on for the A/C compressor to make the noise? The noise is coming from the A/C compressor, the condition known as "slugging" is believed to be due to liquid refrigerant collecting at the suction side of the compressor. As the compressor clutch engages, the liquid refrigerant is being pulled through the compressor. There is no fix and the noise does not indicate a problem or failure may occur. source: http://chevroletforum.com/forum/showthread.php?t=9382 I have the same thing and I don't believe it is the engine. I believe it is the A/C compressor. I had the same thing in a Honday Odyssey that I owned. It was explained to me as the coolant in the A/C system condensing after it has been used and turned off on a hot day. Then, when the A/C starts up again on another hot day, the compressor makes noise as it clears out the condensed coolant when the system starts up. It was considered normal. Given that manual says that the noise will occur when starting out on hot days, it makes sense that is what is going on here. While certainly I have had cars with A/C that don't make this noise, it isn't the first either. source: http://forum.chryslerminivan.net/showthread.php/9312-engine-makes-a-grinding-noise-when-starting-up-sometimes
