i have rg7421 2013 model with quantum pickups..there's a very loud hum when switching to bridge and center selector. i also own an rgr321ex 2011 model and when compared, theres no hum on all selectors. i already brought it to a guitar tech nearby and they werent able to fix the hum. they resolder the wires properly and cleaned the output jack..they also said they didnt see anything wrong with wiring. please help. the only shielded part is the cover itself.