Can’t replicate the noise on the lift, only on the highway above 55 mph. That is why I think it is likely something involving the exhaust when the car is under load. It sounds like it is coming from the engine area but the exhaust flex pipe connects underneath in front of the drivers seat near the engine compartment. Given that it only happens on the highway it is hard to pinpoint the exact location. I don’t know enough about resonators to say whether the sound would travel if the resonator was the cause or if it would be localized to that exact area.