Engine Compartment Sound

[Astro Traveler]

Hi,
I have an '87 Astro with an odd sound coming from the engine compartment - something between a knock and a chafe or chirp and not very loud.
I had a Jaspar engine installed several months ago and about a month ago the sound started.
It only occurs when the engine reaches operating temperature, is barely audible from up top and is much more pronounced from under the vehicle. I went over everything with a stethoscope, sounding each component driven by the serpentine belt and heard nothing there. It seems loudest right behind the crankshaft pulley.
The period of the sound matches the rpm of the serpentine belt but if I remove the belt I still have the sound. I have replaced the serpentine belt, the fan thermostat and the harmonic balancer to no avail.
Turning on the A/C has no effect on it.
One time I pulled in to my garage with the engine hot, turned it off and then started it again and the sound was initially much faster but then slowed down.

I am baffeled by this and looking for ideas.

[chevymaher]

Trans dust cover may be hitting the torque converter bolts. Put spacers in see if it is what it is. I went through that on mine and I had it on a couple other peoples. The tolerance there is close obviously.