moaning/howling sound from parents t&c

My parents have a T&C van, what ever the top model is (not awd though). Anyway, it makes this moaning/howling sound quite frequently. I originally thought it was something with the brakes because when I noticed it I was driving it and sitting at a light with my foot on the brake and it made this loud howling sound. I thought my foot slipped off of the brake a little and caused it. However, my mom says it does it with the brakes on or off, sitting or crusing, even accelerating??? Has anyone else had this problem. The dealer can't figure it out and since it is intermitent it is hard to diagnose. Any help would be appreciated. Please post back to the forum as I won't check pms regularly. Thanks again.

A/C compressor, that is it

The dealer suggested that it had something to do with the a/c. they supposidly fixed it, but the noise came back. I don't know whether they actually replaced the compressor or not, but what ever the did it didn't work.

The Haines' manual of my Mercury Villager says the worn shaft in the water pump housing will make that "howling" sound. I am not sure if the TC is the same but it worths some attention.

If the sound comes after the engine has warmed up, then it is quite likely the water pump. Usually, the van would have some cooling issue along with it.