I have a motive bike. And when i shift in to low gear my shifter in the back hits the wheel. And it jumps gears. When it goes into the high gears it makes a loud nose.
Check your chain---it may be time to replace it ( Check the shifters at EBAY.com [under the CYCLING category-Mountain Bike Parts] ) Switch to SRAM ( X.7,X.9,X.0 ) trigger shifters ASAP----
There are 2 small screws at the end of the rear changer unit that are for controlling the movement of the unit. Set these screws so that your gears are working properly. Good luck.