I've just fixed an annoying squeak coming from my i30 passenger seat and thought I would post my fix here in case any other members have a similar problem.

The noise is induced by bumps in the road exciting the seat frame and transmitting up through the frame into the headrest.

The interface at the headrest uses a plastic insert that fits inside a freely moving part of the seat frame (part of anti whiplash mechanism).
The insert makes a loose fit inside the tubing of the frame.
On my car there was the remains of a thin foam strip that was probably intended to take up the slack and stop the joint from rattling.

To fix the loose insert I first reclined the seat and removed the headrest by depressing the little button at the base of one of the stems.
The headrest then pulled straight out.

With the head rest removed I pulled on the stems to lift them out of the seat by about 4cms to reveal the locking tab on the plastic insert.

I removed the insert by depressing the locking tab with a screw driver while at the same time levering upwards on the insert.

With the insert removed I applied two 1cm x 1cm approx squares of insulating tape onto both sides of the insert and push fitted it back into the seat.

I refitted the headrest, banged on the seat with my fist a few times and HOORAY! no more annoying squeaks or rattles.

Thanks! I found your post very usefull, 'cause I have the exact same problem! THKS again!