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.
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.