So in summary...
Vibrating conductors, with respect to an AC motor starting, are caused by the conductors being forced to 'become magnets not become magnets' 120 times per second. (Sometimes) Violently pulling themselves against the inner walls of the EMT, releasing, rinse repeat. And pulling puching against each other. This is amplified by a motor that starts slow due to reasons such as pulley size or voltage drop. It's amplified by marginally sized conductors. But it's CAUSED by slip.
Vibrating conductors, with respect to an AC motor starting, are caused by the conductors being forced to 'become magnets not become magnets' 120 times per second. (Sometimes) Violently pulling themselves against the inner walls of the EMT, releasing, rinse repeat. And pulling puching against each other. This is amplified by a motor that starts slow due to reasons such as pulley size or voltage drop. It's amplified by marginally sized conductors. But it's CAUSED by slip.