CM2250 loud engine whine, need advice

[JimT]

do you have any background about the truck? know any recent work that was done to it?

based on your post, the videos (the 3rd video seems most distinct) and my own recent experience with a new oil pump, i'd be inclined to agree that it's likely the source of the noise. however more information, if available, might point toward other sources.

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MY new oil pump makes a nice whine. When I installed it I noticed (as someone else on here also said - in the thread Rawze referenced above) that the gear it meshed with had a nice visible wear pattern from the previous pump *** re-read the other thread, seems the wear pattern might not be from the oil pump ***. Functionally not a concern, but it might account for the sound. However, the whine from my engine is most noticeable at idle and usually loudest either standing directly in front of the engine, or most especially standing behind the cab. While driving, or even running at a high idle, the whine becomes less distinct, at least for me. It also seems to be less noticeable after the engine has warmed up, but that could just be me acclimating to the sound.

I guess my point here is that the whine may be from gears, but not necessarily from the oil pump. The fuel pump and air compressor, cam, and idler gears and (like mine) a scissor gear are all potential sources of a similar sound.