Defender TD5 vibrations. Please help.

[wavesport7]

Started driving home this evening and noticed a vibration at between 45-60mph and was only noticeable under load in 4th and 5th gear, did not try a lower gear. It drives without fault otherwise, however after a short while it developed a sound like a budgie(almost a squealing) from the front end and was evident in all gears. After a couple of miles I had to run through a road flood which would have splashed the underneath and the noise stopped immediately! A couple of miles later the noise returned.
My initial thoughts were that the water may have cooled something that was causing the squealing or even lubricated it briefly, although the vibration continued throughout.
Any advice would be very welcome.

Many Thanks.

[wavesport7]

Thanks for posting your ideas. I have just tried your suggestions and can confirm it is the front prop shaft there is play in it and I can also see a broken piece if metal (perhaps something like a thin metal collar or shell).

Many Thanks again for all your help, most satisfying.