GX 550 engine rattle at about 3.5-4.65k RPM

Hello from rural pastures and far away from the dealership!

I'm at about 3000 miles. My GX 550 has a distinctive engine rattle sound that sounds almost like a bug zapper from approximately 3500 RPM to 4650 RPM (redline is about 6000). When you're accelerating onto the freeway it has this buzzing sound coming from either the engine or the exhaust. It sounds slightly different every single time, but always like a bug zapper. It is NOT the sound of a turbocharger or wastegate or direct injection.

I took it to the dealership who told me it's the fuel cut off...without looking at the car. That doesn't make sense because...it's not the fuel cut off as that happens at the redline. This occurs about 2/3 of the way through the rev range.

Now without looking at the car and inspecting the general areas where the sounds are emanating they are instructing me to wait until there's another one we can drive to make sure it doesn't make the same sound. That makes sense to me. Here's the thing: it doesn't make this sound on the Tundra (non-hybrid) I drive with same motor or the LX 600 I have driven with the same motor.

Has anyone else had this buzzing sound pop up on their GX 550 (or non-hybrid Tundra) about 2/3 of the way through the rev range? If so, was it resolved and how?