The silver diaphram look'en thing under the ac compressor, possibly with vacuum lines, is making a clunky tapping noise, the engine is running fine, just concerned because need to use the truck a few more days before fixing, should I be worried, help please.

The truck stopped making that noise the next day when we left from NC to Pa (400 miles). Didn't make the noise the whole trip but now it is doing it again in Pa (running fine though). So hopefully we will not have a problem going back to Nc. I need to pick up a diesel engine repair book to find out more info, espically what that air pump does. Thanks Eric

Vacuum pump? is that what your talking about? When they fail they will make some noise alright.

I think it is a some kind of a vacume pump. It was making that loud noise the whole time (sounds like an exhaust leak) we were in pittsburgh. We put about a thousand miles on it and it still runs fine though. I am going to replace it now though. It makes me wonder that if the engine runs fine what is the vacume pumps purpose?
Eric

vacuum pump provides the vacuum to operate warmup valve at back of driverside manifold, the EGR, and redirect air inside the cab between vent, floor and defrost all done by vacuum pots.

I am wondering if i should replace it or let it go. The truck is still running fine. The vacuum pump is 134 dollars at advance auto. The only difference i notice with it bad is the louder noise. Is it a possibility it is not totally bad? If it goes totally bad will the truck break down? I was wondering if it can also effect the a/c since the a/c light is blinking?

that price you got is for the pump and drive cam assembly minus the pulley.
You can purchase just the pod seperately, 99% of the time its all you will need, and its a lot easier to do that way. Delphi makes a replacement, diesel shop is the est place to get one that I know of.