Sounds like you didn't 'bend' the body around the shifter. Therefore, when the weight and drivetrain flex due to you turning, the shifter comes in contact with the body....
If you look at the directions, it tells you that you need to make sure you have 6-8mm clearance between the shifter and the body, if not you need to do some bending with a pry bar...
When I installed my shifter, I had enough clearance but if I'm doing a u-turn and hard on the gas, it will still come in contact and vibrations reverberate throughout the body making a lot of noise. However I'm leaving mine because it happens so seldom