Engine makes loud knock only on cold start

[Rustyshackleford]

My 4.0 OHV with 219,000 miles makes a loud knock when cold it'll make this loud metallic noise 3 times (knock knock knock) which sounds like rod bearing then purrs the rest of the day nice and quiet. I'm running 10w30 supertech high mileage in it because the oil it came with was black like tar and I wanted to change it out in 1,000 miles or so for better oil. I just bought the truck a few weeks ago. Its louder some days than others but ive put about 130 trouble free miles since owning it. Should I worry if it goes away immediately upon start up? I should also note that I suspect the IAC is bad because it cranks cold and idles around 600 rpm right away without an increase in rpms to warm up and theres an exhaust leak at the "y" on the down pipe if it makes a difference. Thanks in advance

 

[adsm08]

That almost sounds like something is loose and hitting right on startup.

Noises are hard to do over the internet.