I found out by reading the forum that the Constant Velocity (CV) joints at each end of the propshaft should be regularly greased to stop them failing. So that was the next step.
The rear one was very straightforward to access once the car was jacked up.
The front one was much more
difficult. Apparently some builders cut an inspection panel in the
bottom of the car to access it, but the previous owner had not done that.
So I had to take the top of the transmission tunnel and try and figure
out how to do it from on the top.
If you can see the grease nipple from this photo then I'm impressed. It was very difficult to access but by moving part of the wiring loom I was just able to get the grease gun positioned on the nipple.
Fixed for another year.