I sometimes hear a knocking noise on the rear passenger side of my car when I go over uneven roads. The nocking sound goes away for a while, a few days or even weeks, then returns again, so could this be something else besides the control arm/ball joints? Also is if its a control arm/balljoint problem is it easy to fix and how expensive could this procedure be?

First, it would be useful to know what type/year of car you're talking about.
You said "rear passenger side, which exclude a possible problem with ball joints as they are at the front of the car.
Probably causes are multiple.
Shock absorber, suspension links, coil spring, body/suspension mounts, something loose in the truck, and more

Bad Constant Velocity Joint in Rear Axle?

Steve

What, .....is your crystalball fogged up again ?

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2007 C 230 Sport.

If his past posts are any indication, he drives a '00 S500.

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

Yes, I drive a 2000 S500. Also sorry for this dumb question but is the shock absorber the same as the strut?

Well... yes and no. Technically, they are not.
In your case, what you are calling shock absorbers are in fact hydropneumatic shocks. (expensive, I'm sure)
Perhaps a mount is bad or loose?

__________________
It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D

according to the tech it is a faulty stabilizer link causing the sound