Hope someone can help with this - the wife's Fabia (Y Reg estate 1.9 SDI 75K on the clock) has suddenly developed a loud speed related knocking / clunking.

It is linked to road speed and not engine speed, and appears as soon as you drive, getting faster as the road speed increases - very metallic in nature.

Jacked the vehicle up and checked for free play in wheel bearings / drive shafts, and as far as possible suspension bushes etc.

Could'nt find anything wrong, so I ran the car - still on the axle stands in first gear. Could not reproduce the noise, however, if I held one wheel, and let the other spin at twice the speed (via the diff), I could feel a light knocking through the static wheel - one knock per wheel revolution.

Dropped the car back down, and the noise had gone - no problem for about twenty miles - but suddenly its back again.

I am suspecting a bearing here, possible moving in ahousing/ becoming unseated, but have no idea where, unless it is in the diff - I wonder if dropping the wheels down pulled it back into the correct position?

Anyone come across this before - any suggestions what I can check next. All help gratefully received.

there was a known problem with the hub nuts on early models which produces symptoms very close to what you are describing, tried a search?