knocking when transitioning on/off light throttle

[sambb]

Hi all,
I'm getting a front end knock. It happens on dead flat road, happens mostly in 1st but happens also 2nd 3rd etc if your going a little too slow for the gear. If I'm coasting and then just give it the slightest throttle it will knock and then if I back off the throttle again it will knock. Also happens if I take off normally from standstill.
It's not the bar hitting the steering arm mid cornering problem as there's no feedback through the wheel.. Its also not brake related as I'm not on or off the anchors when its happening. It crossed my mind that it could be the rear engine mount, but it happens when transitioning from coasting/zero throttle to just a tiny little application of throttle, so I didn't think the engine could be moving around too much.
Feels almost like backlash is being taken up and then out when it happens. I say this because if I'm coasting down a slight gradient with ever so slight engine braking happening its not as easy to replicate - its really pronounced on the flat. And if I'm flowing along nicely its not there either - its a light throttle transition thing.
checked the anti roll bar mounts and droplinks and exhaust hangers where it turns around the bottom of the fire wall and for any evidence of contact between anything and nothing obvious is there. any clues?

thanks

sam