Another mod for quieting a G4. For $60.00, the modder reduced the decibel level of his G4 MDD from 50dBa to 30dBa. He also lists a quick mod for $2 that will reduce the dBa from 50 to 40—not as good, but definitely inexpensive.

Long article...
http://g4noise.com/mods.php?ID=39&p=all