70 is about 103 ft/sec out tires are 5.7' circumference so 103/5.7=18.07 Hz at 70. 18*4.1=73.8 Hz aka 73.8*60=4428 RPM. That's definitely fast enough to be a problem with a small weight off balance.

I'm a little concerned about the possibility of under load causing an issue but that would be very similar to my theory of my under braking causing vibration.

Do you get UFO noises when backing up?

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)