don't quote me on this but it sounds like the VCM.
Yes, my 2018 Ridgeline does the same thing.It's hard to describe sounds but when I use the cruise control at highway speed, I can hear a low rumble/rattling sound from under the hood. It only happens on very slight incline. If I'm pulling a hill, it goes away. When I'm on a perfectly level road, I cannot hear it. I cannot reproduce it with only my foot. It's almost like the mechanism controlling the accelerator is oscillating. It goes away as soon as I disengage the cruise control. Has anyone else experienced this problem?