Intermittent grinding sound from engine

[mysticclam]

Left a friends house really late last night and it was really cold so I was letting the x warm up before driving home. After about a minute I heard a metal bearingish grinding sound. It wasnt loud and lasted about two seconds. After another 15-20 seconds it did it again abit longer maybe 4 seconds. It went away. Anyway every 15-30 seconds after that it would do it again. This is not a loud sound and never lasted more than a couple seconds. Could this be waterpump. It seems to be from the front of the engine. After a few minutes I drove home. I could tell it was doing it all the way to the freeway then the wind and engine was too loud to hear. When I got home it wasnt doing it anymore. If it does it again what should I do to try and narrow it down. Again its not very loud and is just kind of a chu chu chu chu sound for a really short time. Doesnt seem to be any play in the water pump shaft. It speeds up with the engine too.
This is on a 91 OHV. Could this be only showing up now cause of the cold?

 

[Albino 94LTD]

Clamman, did you have the defrost on?? Could be the AC Compressor?? The cycling on and off is consistant with it.

 

[mysticclam]

on off didnt make a difference Ive been around this truck for 13 years, so its a new sound.
The AC hasnt worked for oh, 11 years so dont think thats it. Its just like that sound a cpu fan on the pc makes when its starting to go, you know it wobles and buzzes for a second or two then is fine for awhile. As long as it doesnt get worse I think Im going to ignor it. Thats if it even does it again.

 

[MrShorty]

From the front of the engine? I would guess one of the many accessories driven by the serpentine belt (alternator, water pump, tensioner pulley). If it were me, I would poke around with a stethoscope to see if I could figure out more precisely where the noise is coming from.

 

[mysticclam]

Yeah, had a guy at work listen to it and he said its identical to what his 91 F150 did a few years ago and it was the clutch on his AC compressor. I think I may just hit the wreaking yard and see if I can convert to a non ac setup since there is no point with my AC not working anyway to be replacing parts of the system.

 

[Albino 94LTD]

I win a cookie!

Turn the compressor into 'on board air'