Any ideas? Please don't say water pump. I just had this engine apart to do a head swap. Idler and tensioner pulleys and bearings are new. Belt is new. Same noise as before I did the heads.

I'm going to pull the fan and clutch to eliminate that next, just not today.

Seems to change RPM with the engine idling steady, and it does it more when the engine is warmed up.

 

Sounds like the fan/clutch!

 

Knocked the fan and clutch off today and started the truck up and the noise is still there. I'm guessing water pump. If it is that, I'm going with the plan of "turn the stereo up and change the pump when it finally starts leaking"

 

Isn't this the Ranger that was in a flood and underwater awhile back?

 

 

Cured!!!!!!

The tensioner itself was worn out causing the pulley to ride at an angle. This made the belt want to ride to the front side of the pulley, putting it out of alignment with the water pump and crank pulleys. The noise was the misaligned belt on the pulley ribs.

See pics for how the belt rode on the old vs new: