rear noise when car isn't warmed up

Read some other posts about clunking in rear end, but ours seems to make a "chugga chugga chugga" sound sometimes before it's really warmed up. Seems to come from the right rear. Our mechanic seemed to dismiss it as nothing, but then they hate to work on vans! I wondered if it might have something to do with the vacuum lines? I've had just about everything go wrong with this van as possible, and I still love it. Have had vacuum problems before, too. Thanks, Kim