I've been chasing this higher rpm/load duck call squealing sound when under load and hot. The power steering pump fluid color wasn't very nice looking, so I changed that, replaced all the bearings in the idler pulleys, had a drip from the water pump, changed that. Still had this **** sound and it was only for 500 rpm, between 2000-2500 then it went away.
I noticed it was under high boost, so I checked all the intake couplers and gaskets, all good, turbo and manifold is newer.
I had replaced the electronically controlled fan clutch with a new hayden unit. The squeal didn't happen on cool days, only warm ones, so I check the codes, and the pcm had a cooling fan rationality code, reset it, and drove monitoring the fan clutch speed. Clutch fan speed was a little off, always lagged for a short while then settled down to commanded speed.
One day I'm driving with a trailer on, and the scan tool plugged in, get the duck call sound from the engine, I look down to see the fan rpm about 600 rpm below commanded, I let off the pedal, then get back into it, duck call sound, the fan catches up to commanded and the sound goes away.
This is a newer fan, I rotated it by hand sounds ok. I returned it, bit the bullet and bought the mopar OEM part. No more squealing duck call. A google search reveals a lot of issues with non oem electronic fan clutches. Lesson learned, use the mopar one, the original lasted 470,000 km's.