No joints at rear ....
If the knocking can be heard when just turning the rear wheel (on jack with car stationery): brakes, bearing or wheel is touching/catching something. Could be the tyre. Have you tried swapping front and rear wheels of that side? (incase you have directional tyres)
If you hear the knocking only when moving, then it's probably a bush or joint (there are several). Could also be the exhaust. There is a shield above the pipe at the rear that can drop.
Oh and don't discount the idea that there is a loose bolt floating around inside the rear trim somewhere ... my first Alfa had a couple of those ... must have been dropped during production and never retrieved ...
The tyres are new and I had the knocking sound before changing to new tyres, so I am pretty sure its not a tyre thing.
Then, I remember when I went to change the tyres, I rotated by hand the rear left wheel (without the tyre on) (the sound comes from the rear left wheel) and I was listening to a sound which didnt exist on the other wheels.
I also noticed that when the car is moving on a steep right turn (where the load is on the right side of the car) there is no sound coming from the left rear side.
As I explained before, this problem exist for more than 15000km and it is still the same since then. (and keeps giving me a headache)
If its a bush, how should I know which bush it is?
Ok..i know that this is a stupid question, but for example, if I
send the car to a service expert, and if there are several bushes
that may cause the problem, how will he be able to find out which
bush is the faulty one?