IMHO parts rattling around in a mobile enclosure are undesirable. However depending on the device very well engineered devices may well have loose fitting components. In fact that may be an intentional part of the design. A classic example is the M16 rifle. It rattles like crazy and is designed that way so that dirt, sand, mud,
etc. that will get into the mechanism do not jam the weapon.
Just a side note on heat sinks in external enclosures. For many years heat was considered the mortal enemy of hard drives, but Google Labs extensive study of hard drive failure concluded there was no provable link between heat and drive failure. I just got a neat little external enclosure from OWC that is entirely made of
plastic and has no heat sink at all. It does have some tiny ventilation holes but not enough for any serious air circulation. I haven't had it long enough to draw any conclusions about drive life, but it works well and costs less that $20. But it does not rattle.
