Broken sway bar or sway bar links.
possible ignition wires/coil, mass airflow, or torque converter clutch failure.
The rhythm probably calms them.
Back in Black by AC DC
possibly your tires or a wheel bearing, listen at lower speeds, if you rock the steering wheel back and forth and it comes and goes it's probably a wheel bearing
The toilet may rock back and forth due to an uneven or unstable floor, loose bolts securing the toilet to the floor, or a worn-out wax ring seal.
I believe that it might be because when you are a baby your mom and dad hold you and rock you back and forth when you cried. I don't believe that all people rock back and forth when they cry though.
There is nothing to it! Just sit on it and rock back and forth!
because that baby could go to sleep
Yes, the particles in a rock do vibrate back and forth, but the movement is very small and not easily detectable without special equipment. This vibration is a result of the thermal energy present in the rock causing the particles to jiggle in place.
The grinding noise you hear are your shocks and struts. If you experience bouncy while you are driving, as well, you should have them changed.
p-waves
Rock