Pump sound?

[Creekhouse]

My new to me 1983 ¾ ton camper special, has a mechanical fuel pump and a mechanical oil pump, so why, when I turn on the ignition in a quiet place, can I hear a small pump running under the truck. I’ve crawled around and think it is coming from the pan, but that would be weird … right?

 

[WebMonkey]

is your truck air conditioned?
if so, is the climate control on ANYTHING other than off?

if it wasn't coming from the pan, i'd say it was the blower at 'idle' speed on an a/c truck

 

[fast 99]

If originating from pan, have seen noisy oil pumps. Noisy enough that had to swap out a couple on reman engines. Replaced them with Melling.

However noises will travel all over the place. Have to be careful with diagnosis. If automatic, a tranny pump will also make noise, that will be more high-pitched [whiny] than an engine oil pump.

 

[SquareRoot]

I mean, it's possible.

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