noisy prop...i think?

after my td5 was crunching into 4th recently...today as I was gearing down...starting to get to low revs..there was a horrible rotating rumbling...quite loud and abrasive..still selecting gears ok and no noise at higher revs..can anyone shed some light on to what it may be...I have searched and maybe..doughnut?...loose prop....uj failure...whats the most likely cause, thanks in advance

Does it make the noise when stationary?

Is the noise soley dependant on engine speed?

Does it change when the clutch is depressed?

no noise when stationary mate...yes maily when engine speed slowing down and no noise in neutral or when clutch depressed ...thanks for reply