Sure do, They set up a resonance and like you said it sounds like another quad is behind you. I drilled some 1/8 inch holes in the bars close to the mounting points (one by the engine mount and one by the upper mount)and filled each hole with as much silicone as I could get in there. This seemed to help dampen the vibration and noise from them.
08 700xx Barker's exhaust, Mod Quad intake, 13t, PCIII with Bo White map, Precision Steering Stabilizer, L8TON Sway bar, PRM side bars, PRM full skids, Pro Armor Dominator front bumper, RAZR2 on front, RAZR on rear
12 RZR XP900