Clanking noise from deployed bow thruster

Whilst motoring forward with my bow thruster down I heard a loud clanking noise. I put the boat in reverse and then forward and the noise stopped. I am guessing that the thruster had not fully locked out. Has anyone experienced this?

I ask because my mechanism got stiff after 3 years. In my case the thruster doesn't always retract, but I suppose the opposite might be true if the flow across the door is high.

I was told not to go over 4 knots, rather than 1.5, which is very slow. We have never had an issue on the down drive, only on the up.

I have had problems with my thruster not retracting properly if I accidentally motor too fast before remembering to retract it. However, the problem has always been electrical i.e. an alarm condition indicated via the LEDs on the thruster control panel. Slowing almost to a stop, turning the bow thruster off (on the main switch board) and then back on again has, so far, always reset the thruster and it has then retracted properly. I have never experienced rattling or other mechanical noises from the thruster, except for a faint whirring noise in the forepeak during raising and lowering