Unusual sound on the 1972 stock

[Silent]

I was just on the bakerloo line first carriage. Every time the train was about to move it made some deep winding, loud sound. I haven’t heard the 1972 stock make this sound before. What might it be.

I’m just curious to what the sound was. I should’ve recorded it but forgot to.

 

[Dstock7080]

Possibly the RPA Rotary Pneumatic Accelerator not engaging first notch and having to rotate again?

 

[73Stock]

Is that the same sound and jolt as on the 1973 stock when pulling away?

 

[Silent]

I haven’t heard the sound on a 1973 stock either. It was like something was winding to help the train to release.