When fork takes hits every now and then a crack almost whip noise. Under close inspection the lower headset bearing rattles a tad do i have the wrong size could this be the cause, or is the steerer loose .

Can you just try and nip up the preload a bit? That noise would usually mean a loose stack.

Do that chunky, still makes a crack , push the bike into a wall with a small amount of gusto and a intermittent crack!!!

Put a bit of grease in the cups and on the bearing.

All the above, but loosen off the stem where it clamps to the forks before you nip up the top cap. Then tighten stem back up.
(Apologies if I’m teaching you to suck eggs)

Pikes?

Pikes they are , 120 mm travel .

They do that – its a creak in the CSU as you suspected. If they are less that 2 years old you can send them back for replacement / fixing.

EDIT: I should say its probably a creaking CSU, but the sound is definitely more crack than creak so its very likely.

Humm, I’ve a set of pikes that do the same. Dangerous or just annoying?

It is a crack like whip noise , thought it was my carbon bars failing.

Just annoying.

Wasn’t there a comment on here recently about curing it with a bearing retainer or similar?

Replaced fork with fresh grease and the bottom bearing rattles , when preloaded wheel push ed into an obstacle the bottom bearing moves . New bottom cup etc I’m hoping will be the cure .