Pedal bikes too. Mostly of the spring-loaded type like this.
This nifty gizmo makes loading and unloading front racks easier by adding a self-centering action. Great for Porteurs and city bikes. Two downtube sizes.
velo-orange.com
The bike quality point is well made. I think cheap, stiff bikes with low geometric trail are most susceptible to this. I had an absolute nightmare of a time getting rid of it on that cheap Chinese pseudo-gravel rig - including a headset change, two stem changes, silly-wider handlebars and several tire changes for more pneumatic trail.
When I started, it would do it at anything over 15mph on 4% downhills and up/down vibration would precess into side wobbles. Which sort of ties into Ghost's frequency question - it depends on the rotational speed of the wheel.
Wooden slat bridge decks were a nightmare, even below 40psi. It was an incremental process after that, including several configurations that would do OK at 20-25mph but would get massive front-back bucking under braking.