Spoiler Causing Vibration?

[A35ME]

Ever since I installed the G35 look spoiler on the rear lid, my 2008 3.5 automatic has vibrated mysteriously. Dealer cannot diagnose, the vibration is felt in the seat and floor. I want to remove the spoiler to see if that's it, but thought it worth asking if anyone has experienced this before I go through the trouble if it couldn't possibly be that. It is definitely not the tires or wheels, those have been balanced, rebalanced and thoroughly checked. Ruled out brakes, rotors, etc. as well. If not the spoiler, my sense is perhaps something in the drive train.

Thanks for any thoughts or comments.

[dangeris]

Ive had my G35 spoiler since I bought it in 10/07. I've never had any vibrations except for when I drift over those dang rumble strips