Vibration in Reverse

This is also placed under the Highlander forum, I've heard the Highlander & Camry share engines/transmissions so thought I might get a wider response in this forum.

My '02 Highlander (50K miles, 4 cyl, auto) recently developed a severe engine vibration anytime the car is placed into reverse. There is no vibration in any forward gear, park or neutral.

Any thoughts, comments and assistance appreciated!

Howard Duncel