Serpentine belt squeals only while loaded and accelerating from a stop.

Here's a new one to me. I've been using my 2011 Off Road, 132K miles, to haul 800 pounds worth of cement bags. Driving to the store everything is completely normal. But, coming home every time I accelerate from a stop the belt squeals. Once I'm going about 20 mph it goes away, and no combination of engine speed or throttle will make it come back, until the next stop. Turning the AC off makes no difference. I'm going to replace the serpentine belt, and I wondering if anyone has heard of this before?

 

Belts should be replaced at 100,000 miles. I replaced mine at 100,000 and thought I had done it at again 200,000; but apparently mis-remembered. Mine broke at 248,000 miles and was a PITA. Was 35 miles from home pulling a TT. Cost me $200 to get it towed home. Called a friend to come and get the trailer.

I'd replace that belt yesterday.

 

I made an account just to reply to this, it might be worth replacing your tensioner. I had a similar issue with my belt squeaking in drive when the AC clutch engaged. Replacing the belt alone didn’t fix.

2018 2.7L @ 160K my tensioner was soft relative to a brand new one.

 

Put a wrench on the tensioner and see if the spring is weak