I’m wondering maybe a pulley/bearing going out.. my work truck, yes different but I had a very odd groan noise when my truck would get around 2500-3500 rpms. (2013 F150). Water pump detonated about a month later. Turns out it was that.. and get this, would only do it while actually driving. I reved it multiple times to 4000 rpms while in park without being able to recreate it.

Could be a handful of things. Idler pulley, PS pulley etc etc.. just my thoughts.

I know you said it doesn’t happen in idle which I find is very odd. Could he that intermittent maybe.
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2010 P7B 150K. 11K hours. 3.27, RKE, Cruise, Ported stock plenum, JMod, ADTR sway bar, KYB rear shocks.
2011 Sierra 1500 155K, too many mods to list. (RIP 01-05-2019)
2001 Durango R/T 5.9. 230K. SOLD 5-1-19

I’m a classical textbook over-thinker.