Clutch pedal has occasional squeak
 

I've noticed a slight (just about hear it from inside the car, more noticable with the window down) squeak when the clutch pedal is pressed or released - but oddly only after a long drive (about 100miles or so plus, in one go). I first noticed it on our summer holiday last year, and again on a few long trips this year.

What's odd is that it seems to cure itself after a rest - the day after the long drive, it's quiet as normal again. Our usual more local day-to-day trips don't cause the noise.

I had the clutch bearing - and therefore also the clutch - replaced about 15k ago. It drives and changes gear absolutely fine, both with and without the squeak!

Any ideas?