New scary noise I noticed on cold starts

Since it's been cold I've noticed a noise on cold starts, it goes away after the truck gets warm. I did a oil change last week with thinner oil in hopes that would help, it seemed to for awhile but I got in this morning and it sounded worse than usual
Any chance someone has ran into something similar?
This is the best video I've been able to get of it
https://photos.app.goo.gl/oCvWgZpP76SrPF67A

 

Welcome to TW -- hope someone will recognize that thumping noise -- I have no clue.

 

Automatic tranny - maybe front pump?

 

Yeah automatic trans, it definitely sounds like it's coming from up front though but anythings possible

 

So with a more careful listen it sounds like you rev the engine slightly and the speed of the noise increases.
I'm now going with maybe a pulley, idler pulley.

 

I would pop the hood and crawl around the truck to see where the noise is louder. an old school trick too is to get a wrench, or anything really, put it to your ear and touch it to where you think the noise is coming from. it will amplify the noise like a stethoscope.

 

Yep. I have a cheap mechanic's stethoscope similar to this. I have also used a long screwdriver which works well.