I have an 03' Z with 27,000 km's. Problem just recently started after taking it out during these warm winter days in Feb.

There is a strong, noticable vibration that occurs through the shifter when I take my foot off the gas pedal and allow the rpm's to decrease from 4,000 rpm's to 3,000 rpm's. The vibration occurs right around the 3,500 mark. Seems to me like this is related to the transmission. Given that this problem only started recently - I can live with it too - I can't quite pass this off as something normal, but perhaps it is.... Anyone?