Roaring sound when towing uphill

My pickup truck is a 2003 Dodge Dakota, automatic 4.7L with towing package. I tow a 19’ travel trailer, weighing about 5500# when loaded. When I am towing uphill, keeping the truck in 2nd gear, between 2500 and 3000 rpm, I periodically hear a loud “roaring” sound from the engine. Rpm and engine heat remain stable, and the sound eventually fades away after about 30 seconds, whether I let up on the gas or just maintain speed. To say the least, this is an un-nerving sound, and I am wondering if engine or transmission damage is occurring. Any thoughts?

Could it be a cooling fan coming on?

My daughters 2003 Montana had that exact noise and you’ll never guess what it turned out to be.

A worn wheel bearing. Weird eh?

I test drove that sucker for a half hour and tried everything imaginable and couldn’t even begin to think that’s what it could be.

She took the van to her independent tech and he diagnosed that immediately. Sure enough, no more roaring noise.

I could have sworn it was a noisy fan too.

Although that may not be your problem, I just thought I’d mention it.

Its either the electric radiator fan turning on (if you have an electric fan) or the fan clutch engaging causing the fan to turn at engine speed (if you have a regular fan). In either case, it’s not a problem since pulling a load up hill is making the engine work harder, and it heats up faster than the normal air flow (that resulting from the vehicle moving forward) accross the radiator can handle.

I’ll be the third saying it’s the cooling fan.