Ideas on what this noise might be from? It matches RPM.

 

Hard to tell.

Sounds like you may have some belt noise. Which is often one of the idler pulleys on the belt driven accessories.
Or
Sounds like you may have a slight exhaust leak at the downpipes? (more of the tick tick tick I'm hearing)

 

Hot or cold or both?
New sound or old sound getting worse or always been there?

 

Both got and cold, new sound, just noticed it yesterday for the first time. I crawled underneath and can see coolant leaking from back of engine presumably from the head gasket. Temps have been normal at 170-188F.

only two things that have happened which I can think of is I changed the oil and put 5w40 rotella t6, and I ran out of gas and cranked it over awhile after putting a gallon in only to realize i needed a few gallons to get it to start.