Ticking Tyre, driving me nuts

[karona]

Ever since we had the summer tyres swapped for snow tyres on the same (steel) rims a week or so ago one of the front tyres 'ticks' as if there's a stone stuck in the tread blocks. So far I have:
Checked for stones/nails stuck in the tread blocks
Removed the wheel and checked the brakes, pads OK, callipers working properly, anti rattle clips in place, backplates clear of the disk and no stones/muck stuck to them.
Spun the hub with the brake pads out, silence, no movement/grittiness in the bearing, and no noises from the driveshaft/CV joint.
Refitted the wheel and correctly torqued the wheelnuts (the tyre place must have a tame gorilla trained to tighten the nuts with a breaker bar)
The wheels have plastic trims held on by the wheelnuts, they are secure and don't rattle.
It still ticks.

I swapped the wheel for the spare (summer) tyre: silence! Swap them back: the tick is back! So it's definitely the tyre/wheel that's ticking, any ideas as to what could be causing it would be very welcome. Could the tyre itself be faulty? (Michelin Alpin)

[Snowboy]

Badly fitted weight that's flopping about?

[LuS1fer]

Can't see your profile in work - does it have tyre pressure sensors inside?

[karona]

Snowboy said:

Badly fitted weight that's flopping about?

Now that I can check in two minutes, be right back.

[karona]

LuS1fer said:

Can't see your profile in work - does it have tyre pressure sensors inside?

nope, there's no sensors. It's just a lowly Kia Crateo

[karona]

karona said:

Snowboy said:

Badly fitted weight that's flopping about?

Now that I can check in two minutes, be right back.

By the power of PistonHeads, the shortest thread ever!
The weight was squeezed into the bead and must have been tapping the wheeltrim as the tyre deformed.

Thankyou Snowboy

(DOH two bloody hours I spent looking for a wobbly bit of lead!)