I have a pair of Definitive StudioMonitor 450 speakers, which I got less than a year ago. I got them for a very good price because they were floor models, thus I didn't get them new. A few days after bringing them home the speakers started rattling. This usually happens whenever I play a song or album with high bass levels. I keep the eq flat on my receiver, and don't listen to them at excessively loud levels. The rattle even happens when I'm listening to them at a very low volume, and I often have to turn the volume down to a very low level before the rattling stops. This doesn't always happen. I don't get a rattle when watching TV, or when listening to certain albums, but it still happens with most music I listen to.
Loudspeakers Digital Sources Accessories