Drive shaft noises are not uncommon. Usually caused by the nut not being tight enough at the wheel end. Corrosion develops where the shaft can move around, but allows enough movement to knock..

Easy repair though, just remove the nut, spray copious amounts of WD40 (or another brand) and gradually work the shaft till it can move freely again. The retorque the nut and job done.

(When working the shaft, dont forget to pay attention to the ***** too }