noise on cold start up


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Oct 1, 2023
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Mosinee WI
This just started happening wondering if anybody else has heard this. When motor is cold after setting overnight it has a sound like a hyd pump cavitating just for a split second on start. It never does it again until it sits overnight. I live in wi where it is not that cold yet. If it would be -30 I would expect it. Any guess as to what it may be?
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Still trying to figure it out. There is no power steering pump that I can see. It does not have a lifter tap sound. Wondering if it could be the oil pump starting or pump in the transmission. It runs and shifts great. Could it be the flapper in the exhaust? Can not start the truck with the hood up but it sounds like it may be coming from underneath someplace. I made an appointment with the dealer to check it out hope it is nothing.
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I had this happen several times when I was hunting in ND in October. Sounds like a squeal right after rig starts. Only seemed to happen on the nights we got frost and 30 degrees. Wasn't super cold yet.

We finally cooled off in AZ and while it isn't really cold, I had it happen the other day in low 40s.

I thought it was the belt slipping for a split second, but never got around to checking tensioner.

I know it's not the exhaust valve cause I removed it when I added my Magnaflow can.

Leave the hood open and do a remote start and see if you can get a better location.
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Well after searching different sites I found sound clips. It turns out it is the new style oil pump purging the air out and replacing with the engine oil. All is normal.
Thanks for that information. Glad you were able to find this. Does it seem like colder weather is what triggers it more often?

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