Radiator noisy even after adjusting valve

I have a new, tall 4-column vertical radiator that was fitted in the summer. Now it's on a lot I'm noticing it's very noisy. A sort of rushing, whistling noise like you sometimes hear from hot water pipes.

I've tried adjusting the valve (Honeywell Valencia I think) but anything other than off, it is still noisy.
Listening carefully, the noise does seem to be coming from the radiator itself not the pipe/valve as I can hear it all the way up the radiator.

My other radiators (mostly old panel but also some modern columns) don't have this effect. If I recall it is plumbed in using new modern plastic though it has chrome up-pipes from the floorboards.

Could it just be a 'feature' of this rad? Or are there other causes I could diagnose and address?

 

Air, try bleeding it.

 

Tested, it was totally full.

 

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