new vibration

My xj has a new vibration that starts about 15 or 20 mph, and stays to at least 50 or so. It only vibrates while on the gas. While coasting, it is as smooth as before. I was thinking u joints, but the drive shaft seems tight( no movement ). Also there seems to be a new scraping sound on occasion, this is at low speeds after making a stop. The sound seems to be somewhere between the middle to the rear of the jeep. Any ideas?

Jeff

did it come out of nowhere or did you mess with your suspension any?

It came out of no where. Parked it in the driveway-no problems, Took off three hours later- vibs.