That's weird, because I have just noticed exactly the same thing on the drivers side front.
Get a knocking noise when pootling along in first at engine idling speed.
Nothing loose as far as I can make out.

 

You say knocking, could it also be called a ticking like a stone in tyre noise?

Reason for saying is I had this type of noise few weeks ago, turned out it was my alu tyre valves, one on the front had can slightly loose, mde this clicking sounds, tightened it up now and its fine.

Just wondered if you have these alu valves?, mine were Richbrook ones.

Maybe a help don't know.

 

the fronts can go, although its more likely to experience this over speedbumps etc. you say on approach to lights? under braking is it?, a lot of the brembos etc are "clunky" and it is normal and nothing to worry about

 

Might be ARB bushes or drop links.Good luck.

 

On my car, there is no noise over humps or on braking or turning - just when idling along in first.
It is slightly un-nerving as it seems illogical, which is why I was surprised to see something similar in the OP.

 

i also have the same issue

 

Sounds like shocks to me.

 

I have had two replaced on the back and one on the front Subaru shocks are not fit for use

 

I suspect you may be right, in which case I will wait for it to get a lot worse