Im thinking about taking my truck to a shop just for them to tell me whats wrong but im going to try here first.

At idle only I will here a thumping noise coming from the engine on to be what sounds like the passenger side. It has never done it when I first crank it up, seems to make the noise after I have drove it for a little while. Whenever I pop the hood, it never makes the thumping noise so its kind of hard to pinpoint right now.

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2002 3.0 Ford Ranger 4x2, Auto, 250k miles

If it doesn't do it when you pop the hood, it sounds like you might need to adjust your hood alignment. Check to see if the paint is scraped inside the fender where the hood lies. Might need an adjustment.

the hood alignment is good. Im not sure how that would cause a thump at idle speeds. I wonder is altonators can make a thumping noise?

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2002 3.0 Ford Ranger 4x2, Auto, 250k miles

Maybe a hood bumper isn't adjusted right allowing the hood to move around when it's closed

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2021 F150 5.0 Screw

Past:18 F150 2.7, 16 F150 5.0, 14 F150 5.0, 07 F150 5.4, 03 Ranger 4.0

Master Certified Ford Parts / Warranty Admin

but wouldnt it thump while the truck is in motion then?

I only hear the noise when it is stopped and running. But again, it doesnt always make the thumping noise.

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2002 3.0 Ford Ranger 4x2, Auto, 250k miles

Is it a really light knocking kinda noise?
I had this noise and because I recently replaced the clutch I thought maybe something was coming loose or the engine was in its beginning stages of going south! lol
Turns out my water pump had a mile of shaft play in it and for some reason didint leak a drop but made a light knocking noise because of the play.
I thought the pump was the cause of another screech noise Ive been having but today after using a doctors stethoscope ive got it nailed down to my power steering pump which doesnt leak either! lol

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1993 Ranger XLT 2WD Standard Cab Shortbed
3.0 V6 5-Speed Manual
162,000 Miles