teapot sound behind dash

I have a 2003 dakota at my house that is making a teakettle type gurgling noise behind the dash. It only does this when the truck is running. I am thinking that there is a vacuum leak of some kind but I am not sure and figured I would ask other Dakota owners if they have had similar problems.

Maybe this is the PCV valve rattling. That happened with my 5.9L.

Low on engine coolant / possible air the the system?

Noise behind drivers side dash.

I noted that with the engine running the PCV rattles at a pretty good clip. Under the hood it is ridiculously noisy.

I pinched off the vac. line to it and it seemed the noise went away so I changed out the PCV. I am not hearing the noise at this time so we will see.

does it have ac?