[Remford]

We have a 2018 2.3 AWD that recently has started making an intermittent buzz or rattle coming from beneath the car when applying the accelerator while the car is in motion between say 20 and 50mph.

It happens often enough to be really annoying but not to be consistently repeatable when taken in for warranty service. One TSB called for a transmission reflash which they did before promptly handing back the car within the hour and claiming the phenomenon couldn’t be replicated - until the ride home, of course.

Has anyone experienced something similar?

 

[Exit32]

An buzz or rattle from under the car could be caused by a loose heat shield somewhere on the exhaust system. In engineering, the noise is called "acoustic resonance" and can present itself intermittently.

The heat shields are there to keep hot exhaust-system components -- especially the catalytic convertor -- from burning anything that happens to be under the vehicle (e.g., dry grass in a field where the car is parked). Quite common for heat shields to loosen and vibrate. Should be covered under warranty.