Both my G series machines do this as well, and its usually when the head is right down on the carpet, I think its the spring that holds the gear teeth against the driveplate gets weak and causes the joint to slip occasionally, but I may be wrong.

The noise is annoying and its like a loud clunk when I push the vac forwards - but its only intermittent.

Its not the continuous clicking noise that results from a worn actuator lever either.

Its a random, single, loud clunk that only seems to occur when the tech-drive is under load pushing the machine forwards, and it doesn't do it when the head is raised a little and the machine then moved forwards.

What do you mean by the "cam" assembly Beko?

What I'm talking about is the large "differential" cogwheel on the wheel spindle, (Left arrow below) which, when you put it in drive, has a smaller toothed driven cog (right arrowed below) pushed into it by a strong spring - like gears meshing on a car gearbox. I feel the noise comes from the smaller meshed gear jumping out and then immediately back into the large cog that's meshed directly to the gearbox. SOunds complex and I do get fed up of people saying - oh its cos of the cam actuator lever getting worn - this is not the case here as the noise is not a continual clicking in neutral - this noise is in Drive only when pushing the vac.

It only seems to make this occasional clunk whilst being pushed forward, and not usually in reverse.

The fact that both my G series do this means its probably a common problem, and the picture below shows the two gears that I think are responsible for this noise, as the arrowed gear on the right jumps in and out of mesh with the gear on the left, whilst the vac is being pushed forward under load:

My understanding of the usual problem with the clicking noise IN Neutral when pushing forwards OR backwards, is that the actuator lever (below arrowed) gets worn, so fails to hold the driven gear - against spring pressure (above arrowed right) away from the drive gear (above arrowed left) on the axle.