Yup, prop UJ is my guess.
Ive just had one go, which started as a squeal when setting off, then developed into a shiatsu back massage at 50mph.
New one only lasted 3 weeks before I destroyed it on the rock crawl at Frickley.
They are straightforeward to fit, to check, chock the wheels, h/brake off, car in neutral. Get underneath and holding the end of the propshaft next to the joint try to waggle it up down/side to side.
If theres ANY noticeable movement, its a gonner.
Repeat on all 4 UJ's
Replace the joints that are bad.
Ive just bought a Landy joint as a spare, theyre about a fiver each.
While you are under the car, measure the diameter of the UJ bearing caps, and the width of the UJ(across the flats of the bearing caps) There are 2 Landy size joints used, and you can bet they'll ask you the size.
Saves going back under the car doesnt it... :D