The metal ring is a round spring, that should form a tight fit around the spindle.

Rearrange it to fit properly and press it down.

Martin

Hey Martin!

Thanks for your help, that worked perfect!

Now the new belt works great, but machine is still noisy, suspecting it needs some oil, but if anyone has other ideas too that would be great! Also I'm not really sure where to apply the oil.

Then I got new power cables and phono cables to replace the old ones and I've got kind of an idea what to do, but some clear instructions would be great too!

Check the motor suspension.
The motor must hang free in the springs - the metal "ears" of the motor bracket must not touch the nylon bushings - just hang close between them.

Martin

Is that on the bottomside of the turntable with the cover removed, where the power wires and stuff are, or the top side with the turntable platter removed?

Underside.
But you need to have the Beogram the right way up to check it.
Lift it and look up from below. 

Martin

I think I get what you mean, but I'm not 100% sure. I'm guessing the Metal ears is referring to the metal pieces that I've high-lighted in blue in my picture below? Or is it the two metal pieces to the right int hat pictures? I'm also guessing that the nylon bushing is the part I've highlighted in red. Do correct me if I'm wrong ;)

Anyways the motor does not seem to be hanging free so I think what you're saying is right. I remember holding down on the manual adjustment knob while the turntable was spinning and the noise would disappear.

Thanks for your time!

No.

The motor is bolted to the metal bracket.

The whole bracket with the motor, speed selector mech. etc. are suspended as a whole.

Look a bit further away from the motor and lift the motor a bit and you will see, how the suspension springs etc. are supposed to work.
A spring a set of nylon parts are visible to the extreme left in your last photo. 

Martin

Ahhh, I get it now.

I always think of Nylon as a cloth like material, but I forgot it can be hard plastic as well :)

the motor bracket (the one you mentioned) is definitely resting on the bottom nylon part.

Now how do I fix it? :)