For months, I have been experiencing several crashes daily with my DSL-502T (as previously supplied by Telecom). Having heard clicking noises from my speakers, I decided to try clip-on ferrite cores on the DC power lead. I fitted two as close as I could to the power input, with the cable looped such that it enters the core, passes around and through again.
Since then, no more crashes although the clicks are still there and seem to be caused by thermostats.