the previous owner put in a short shifter on my gsr.... i have a known rattle ( ringing) that is associated with short shifters.. any tricks to fix this sucks being on the free way and you have to crank up the tunes

 

jack up car
look at shifter to exhaust contact points and bend exhaust hangers to lower the pipes to avoid any contact.
it may not touch when you are under there, but must touch when it rattles.. as it heats up or whatever.. so be sure to get clearance in there around the shifter lever bottom piece.
good luck.
my shifter linkage was the problem, the 4 inch piece extending toward the back of the car was tapping/rattling on the resonator in my catback.
that could be the problem you have as well. same solution... bend the hangers.

be sure to check clearance of the muffler to bumper as any changes can make them coem into contact and you may melt or burn your bumper...

 

thanks alot for awhile i was thinking damn am i the only on here that had this prob