Front wheel knocking,, what can it be?

[thunderace]

the knocking stops under braking, whether it stupidly light braking or heavy braking

It's either loose calipers/pads or a bearing issue IMO then.

[Wozza]

If you hold the front brake on and rock the bike back and forwards do you hear the knocking? If so check for play between the brake disc rotors and carriers.

[tanuki]

headstock?

[angry_rob]

As stated before check for play in the bearings and headstock. Also I had a similar problem not too long ago, which was because of a combination of sticking brakes and warped brake discs. I've rebuilt the calipers and there's no clicking any more (not to mention the brakes feel 10x better) even with the same warped discs.

[vr46]

Have you got a front wheel stand? can you hear the clicking if you spin the wheel by hand?

[amorti]

If you hold the front brake on and rock the bike back and forwards do you hear the knocking? If so check for play between the brake disc rotors and carriers.

My t595 did this, I thought the steering bearings were no good but in fact there was just play on the disc bobbins.

Also check for loose brake pads, and the classic mudguard brackets.

I've also seen real stupid shit like a stone in one of the brake disc drillings making a noise as it went round.