Same question as Tr!p?? There are a set of rubbers that are almost like pucks mounted on the frame that you should check. The tank has a set of "cups" that should slide onto these pucks when it is mounted on the bike. If these rubbers are in poor condition or missing, it would certainly make for a noisy ride... To check them you will have to likely remove the seat, remove whatever bolt that holds the tank to the frame at the rear and lift the back protion of the tank a bit while sliding it backwards. You probably will only have to slide it back a couple of inches to access the rubbers and check their condition.
Refer to this site (
http://www.bikebandit.com/houseofmot...shadow/o/m2846) and go to the "fuel tank" schematic. Number 19 on the drawing are the rubber "pucks" i'm refering to.
Hope this helps....