hi got a quick question about my freelander 1.8 petrol

when idling or sat in traffic well basically whenever im stood still there is a knocking noise of some sort coming from the engine.
You can not hear it while driving, only when your stood still,
the engine has 76000 miles on it so im thinking about doing a service on it sunday to see if that helps.
It has been been converted to 2wd probably to save the engine but i can deal with that
there is no power loss or nothing just the noise, can anyone help to find the source of the problem.

CHEERS

 

I'd be checking oil level and pressure