Clunking around headtube area when pulling on bars out of the saddle, what...

[Pedal Castro]

...could be the cause?

Very difficult to isolate as I cannot replicate the sound off the bike by pulling/pushing the bars.

It started about 200 miles ago and seems to be slowly getting worse, i.e. more noticeable with less stress put on the front end. Could it be headset wear? I've not had an integrated headset before so I don't know what a worn one would sound like.

[Ham]

Has to be bearings, I would have thought

[Kim]

Test for a loose headset is to hold the front brake on hard and attempt to rock the bike forward and backward.  If it clunks, it's loose.

The other classic headset wear symptom is notchy steering.  How does it feel if you lift the front wheel off the ground?

[loadsabikes]

I'm away for a few days, but could look at it next weekend if it helps.

[Pedal Castro]

Test for a loose headset is to hold the front brake on hard and attempt to rock the bike forward and backward.  If it clunks, it's loose.

The other classic headset wear symptom is notchy steering.  How does it feel if you lift the front wheel off the ground?

I tried both those tests which were fine, hence the mystification.

[Pedal Castro]

I'm away for a few days, but could look at it next weekend if it helps.

Cool, I will loosen and retighten the headset and stem and see if that helps first, if it doesn't I'll see you next weekend 

[Ripio]

Loose hub bearings?
Hard to isolate noise/movement being from headtube area, especially when riding out of saddle, could be coming from further away areas of bike.

[Blodwyn Pig]

could be bottom bracket, and the vibration travelling up the downtube, also I had the very same thing, and it was  2 spokes clacking where they cross, try a different front wheel would be my first bet. Slved the issue my rubbing emery cloth twixt spokes, and then a wee dob of vaseline.