Jackhammer noise comiing from rear

I have a 2001 Pontiac Montana. I sometimes hear what sounds like a jackhammer coming from the auto leveling compressor. It only does it when im at a stop. Just wondering if anyone else has this problem, and if so, what is the fix?

You might have a leak developing. You could check the fittings under the van including the tubing and the shocks. My old Venture made that noise and I tended to think it was fairly normal as it had done it since I bought it. It may be a sensor issue that is detecting a change in the load of the van when you are stopped. Other than that it might be a normal occurence if it only does it for a short amount of time and then stops. If it keeps on making that noise for a long time, then I would suspect a leak.