smosh I think its for 05s thru certain 07s, a VIN range.
A rattle/click type noise near the front of the dash, usually drver's side. They pull out the dash top, insert a couple isolators where the front of the dash hooks into, re-assemble dash. Takes about 19 hours. I recommend people turn up the radio and ignor the rattle...or when you can actually duplicate the noise bring it in to your favorite dealer and have them look at it.
Dont tell them you heard about it on the interweb. They might think you think you are hearing things because you read about it on the interweb. Kapeesh?
edit: Legacys and outbacks, Not Imprezas, Foresters, Tribecas, Bajas, or Justys.