As I was thinking about these other comments I’m remembering a couple of years back when my wife started reporting a really eerie, weird, droning sort of a noise coming from our van. It was weird - sometimes hummed, sometimes droned. Hard to place as many noises are.
It turned out that one of the roof rack cross members was loose. It took me a while & quite a bit of driving around to figure that out.
I’m not saying to check your roof rack - although you might. But basically check anything that might catch wind and produce noise, including under the car.