I was driving my gdads is220d on sunday and noticed a very strange sound when steering the left at 60-70mph....however going straight or right...was fine.
took it to the dealer in leicester and they said they wheel bearing has gone, and that it needs repacing under warranty...
also mentioned the rattle noised from the gear stick area.
couple of months back i took it in, i said that the car is steering slightly to the left, they checked it out and it was disalined, they tracked it £80, 2 front tyres x2 £100 and replacement 2xalloys under warranty free :-)
pretty happy with the service