Exhaust Drone at 55 mph

[d3sarius]

I have a 2021 Laramie with ecodiesel and the 3.21 rear end. I’ve noticed since I bought the truck new in November that there’s a drone sound that is very audible right around 55-57 mph when in 8th gear. If the truck changes RPM or gear, it disappears. It sounds intake or exhaust related, (a resonant frequency) because it comes from the passenger side of the engine bay. It’s not a rattle, just a mid-toned hum.

I haven’t seen anyone else mention it. Truck has been problem free, and I just turned over 11,000 miles.

 

[d3sarius]

Just to close this out, I discovered that my truck had a broken A/C compressor bolt from the factory. I noticed my A/C compressor rattled a little bit from the day I drove it off the lot. Found a loose bolt caused by stripped threads. I ordered a new A/C bracket, put it on yesterday, and the truck is much quieter. The drone at 55 mph is gone, too.