My 03-plate 1,8Tdci has begun to judder briefly as it fires up when starting. This has been gradually getting worse. The car is coming up to 100K miles and has been regularly serviced, mainly by a Ford garage. The last service was at an independant in April when the fuel filter was changed and I fitted a complete set of new glow plugs last September. It doesn't shake unduly when it's turned off and seems to run as sweetly as it ever did. Any suggestions as to the cause would be appreciated.