[TerraMex]

Er, no, it's safe for hard drives,
it would take a very large magnetic (and powerful) field to harm a hard drive,
or jump a bit on it, or even interfere considerably with the operation of any pc equipment (mobo , graphics card). And hard drives have some shielding to them.

In that, two things, to make things clear.
It interferes with CRT monitors, specially badly shielded ones. Can cause damage over time (months).
It interferes with pc hardware, but does not hinder their function,
as it does so in a very very small way, negligible

if it was that harmful (and, let me be clear, it is not),
we'd be seeing hardware drop like flyes with the WC gang.
personally i had two 1048's, a maxijet and a sicce, now MCP600,
and still no "bzzt" effect, even on my super old seagates 40Gb,
after considerable pounding. Monitor yes, rest no.

A cage is a good ideia, but,
remember, not possible (by our standards) to block a field, only conduct it.
you will need a good material to do so (permeable to magnetic fields), aluminium is not that good.
any metal that mas magnetic properties (magnets get stuck on it) is good.
usually , something luike MuMetal, uses nickel/iron, or steel sheet,
and of course, should be connected to the metal atx case.

else, distance the pump from monitor (field reduces considerably by distance) if you get into any problems there.