Squealing noise only under heavy load at 3000 rpm - what is it?

Background: 2011 DCSB Off-Road V6 Auto w/ 160k miles. Only owned it a few months.

I'm getting a squealing noise when the engine is under heavy load around 3000 rpm. By heavy load, I mean the only time it happens is when I'm towing my boat (just over 6000 lbs) and going up a slight hill (there aren't any big hills nearby to try it on). Typically I'm doing around 40 mph when the noise happens and it remains while I stay on the gas. If I let off the gas the noise ceases immediately.

The noise doesn't happen when I drive the truck empty or when it is in park, which is making finding the noise really difficult.

I figured it was some sort of drive train noise and I worried it might be a gear squealing, so I went ahead and changed the fluid in the rear diff, front diff, and transfer case. No change.

I'm wondering if it might be an exhaust leak that only happens when the engine consumes a lot of fuel (i.e. heavy load) and thus has higher pressures in the exhaust? I'm not sure how I would find an exhaust leak like that.

Any ideas?

 

Grease them u joints!

 

Is it a sqeeeeeeeeeeeeeeeeeel or a fast squeek, squeek, squeek, squeek, squeek?

 

its your truck crying for help towing a 6k pound boat

 

I'll grease the u-joints and see if that helps. PO said he replaced them not too long before and they looked to have plenty of grease on them, but that's an easy thing to try.

It's a steady squeeeeeeeeeeeeeeeeeeeeeel until I let off the gas.

 

Check the rubber on the carrier bearing.

 

LOL. From seeing what everyone says on here, I wasn't sure how well it would do. I've been shocked at how well it does. Never had a scary moment and it tows well. Very rare that it will downshift two gears, usually just cruising along and it might downshift one gear for an uphill. Now, I only tow it 5 miles (each way) from the storage area to the dock and the max speed limit is 45 so it is a fairly easy tow. Braking is really good too, but my trailer does have 4-wheel disc brakes so obviously that helps.

 

Maybe belt slippage? When was the last time you changed your serpentine belt? I had the same squeal when ever I got on the gas to merge into traffic. Replaced the serp belt got rid of the squeal.

 

I'll give it a look tonight. PO said the carrier bearing was replaced not too long ago. Anything in particular to look for, or just the typical torn/cracked rubber.

 

I've only owned the truck since May, so I've never changed it. I did look at it and it looks to be in fairly good shape (can still read lettering on it, no cracks or missing ribs). At first I thought belt or pulley, but I don't know why it would squeal only when I'm towing a trailer and not with an empty truck.

 

See if there’s a lot of up and down play in the rubber and evidence of rubbing on the rubber.

 

Coming from the front of the truck?
My '83 would squeal when the front pinion bearing was crapping out.

 

Sounds like what mine is doing also. Only under load too. I was told it might be a belt or a tensioner. I still haven't checked it out.

 

Haven't been able to pinpoint it. Either it is coming from the middle or I can't pinpoint it. I need to have someone stick their head out the window while it does it. While towing I try not to get too distracted trying to check other things.

 

I've had that same sound intermittently under various outside conditions. It's always around 3000rpm and not speed dependent. Did you ever pinpoint what it is?

 

Not yet. Took wife's SUV last time we pulled the boat. I greased the u joints and am hoping that did it.

 

That's probably a good idea. I'll try that as well.

 

As a follow-up, I finally towed the boat again. I'm pleased to report that the noise disappeared. Either the noise was heat related (we are a bit cooler now, but it was still in the mid-80's) or the u-joints needed grease. I'm going with the u-joints needed grease.