MOT Shaker Plates

[Plu Tony M]

997.1 MOT today and noise reported (knocking/cracking) when on shaker plates. Noise was coming from drivers side rear but no evidence of wear or movement in suspension or hub struts etc. After brake test, noise was no longer there. My feeling is that it may have been a brake disc grabbing as this is evident when the car has been washed, as it had before test, and handbrake applied without fully drying out.
Anyone else had similar?