At the risk of really showing my age...
I recall back in the early 80's working on a VAX 11/780 with disk
drives (RM80? http://hampage.hu/pdp-11/egyeb/rm80.jpg) that were
about the size of a washing machine. If you ran a program to seek
the disk heads back and forth from the innermost to the outermost
sector, at the resonant frequency for the cabinet, you could get
the entire drive to "walk."
Believe me, you would notice if one of those behemoth's crashed
into you.
