Dave there is a recent post at Audioreview.com for Rogue 99 where they did the same thing with the sand, said it eliminated small hum from power supply, and surprisingly improved overall sound to boot.
Tweak for Rogue Preamp Owners
Mark O. contacted me and said they are now drilling a hole in the outboard power supplies and are providing "corks" for the hole.Fill the power suppy with sand and it makes an already quiet tube preamp into a super quiet tube preamp.Mark said it reduces floor and tube noise.You guys that have a "older" Rogue can do this your self.Just make sure you remove the cover first so you dont drill through something kind of important!!! Contact Mark if you need some assistance.I havent done mine yet but will soon.