Gramps always warned that rock 'n' roll would cause permanent damage, but it may be gramps who ends up suffering the consequences.

A Michigan State University study found that iPods, those ubiquitous portable music players from Apple Inc. (NASDAQ: AAPL), could interfere with implanted cardiac pacemakers. Electrical interference was detected half the time when the devices were held to the chests of 100 subjects with pacemakers, as far as 18 inches away from the chest, and in one case caused a pacemaker to stop functioning altogether.

Scary, huh? Of course there's no reason just yet to start tossing iPods onto the bonfire or e-mailing warnings to everyone and his uncle. It's only one study, and the lead author of the study is a high school student from Okemos, Michigan, though he is the son of an electrophysiologist father (who gave him the idea for the study) and rheumatologist mother.

As some have pointed out, however, pacemaker patients don't tend to be iPod users these days. A little caution never hurt anyone, but neither did a little common sense.

This story reminded me of the recent warnings about wildly popular Crocs (NASDAQ: CROX) posing a hazard in hospitals (as well as more recently about Crocs and escalators). Yet when I visited someone at the hospital last week, I noticed that the colorful plastic shoes were quite popular with the nurses. So who knows?

Not that these stories necessarily fall into the category, but isn't it funny how the most popular products always manage to spawn urban legends?