most common reason for knocking noise is the cv joint which are available on there own and easy to replace if your mechanically minded this will most likely be the fault but also the ball joint can also have the same effect to again easy fix just get a complete new bottom arm if the ball joint is again at fault but any garage in your area will confirm this for you foc and quote you for the work
Could be rear spring or s/absorber . Another cause which might seem strange , is the rear seat catches . You think it's rear susp rattle , but releasing seat from catches verifies if that is cause . Easily fixed by putting a bit of insulating tape over bar the catches mate with .
Check that with the catches .I got caught out with it years back with a family members car and swore blind that it was susp. noise and spent hours trying to locate it , before a mate told me of catches .Couldn't believe it , but he was right .I released rear seat and tilted forward , road tested and noise gone .Done many cars after with same noise .