What is this for?

Hi guys and gals,
I have a Freelander 2 56 plate and I have been getting a knocking from the O/S/R wheel when going over speed bumps. I have completely emptied the boot, so that it is completely clear, but when I took it for a drive the knock was still there. Being a bit baffled, I checked under the car for any loose or broken parts like exhaust mounting etc, but all is solid. I then came across this rubber stopper on the shock absorber that I found loose on drivers rear but passenger rear was completely solid. I am now thinking that when going over the bumps, it is hitting the shock absorber and making this metallic knocking as there is nothing else it can be. Can anybody please tell me what the purpose of the part circled red is in the picture?
It would appear that it is part of the shock absorber unit itself and cannot be replaced. Your help is appreciated, cheers.

It's a harmonic damper. It's common for there to be over a dozen of them spread about a modern vehicle.

Nodge68 said:

It's a harmonic damper. It's common for there to be over a dozen of them spread about a modern vehicle.

Click to expand...

Thankyou. I thought it was some form of stopper of some descrioption. Do you know if they are changeable on their own or is a complete shock absorber? The drivers side is loose and passenger is solid.

Certainly looks as if the rubber has unbonded from its steel shaft

It's available separately. It bolts onto the shocks string pan.