just installed a short thro shifter and there is a rattling sound coming from where the lever is when the car decel's the rattle is loud but when i press the cluth while decelerating the rattle goes away i can also feel it in the lever when it rattles in sequence....can anyone help me please

 

The bottom of the new shifter sits lower than the bottom of the old shifter. While the engine is under load it shifts back and pulls the exhaust forward in the car a little bit. The combination of these two means that the shifter is rattling against the exhaust when under load. When you push the clutch pedal you're releasing the load from the engine and it rocks back into place and gives more clearance for the shifter.

Using harder motor mounts or inserts would decrease the amount the engine moves and possibly solve your problem.