Air Pump on a OM366LA

Hi again, sorry for all the questions about my engine but the air pump is making a bit of a squealing under load at idle (goes away when the pressure relief valve operates or RPM's pick up). At first I thought I needed the belts tightened but they seem to be pretty tight. Also I ran the truck for a few minutes after bleeding the diesel from the filter change and noticed the top portion of the air pump was already pretty warm. It looks like it may be lubricated/cooled by the engine oil? Should I just tighten the belts a bit more or is there something else I should be looking for?
You might try a beltdressing to see if its squeak eliminates. That will at least confirm whats squeaking.
If belts are properly tight. Maybe take off its belt and check for anything loose or bearing problem. Otherwise if seems all OK, I would not do much other than assure all is tight, belt is fresh & live with its squeak...

Right, that compressor will get quite warm, and it is pressure lubed from the engine. Return oil simply drains back to oilpan.
Check all belts. I have chased that squeal on the compressor/power steering pair only to find tightening the other belt stopped the noise, even though the noise seemed to be related to compressor operation.