I have Mercedes ML350 2007 model with 134000 kms and since last month I am experiencing some light vibration (sensation) and low humming noise while turning steering, which I have been ignoring it all this long. Two days back I noticed that power steering is becoming hard to turn after 15-20 minutes of driving, before I loose it completely I thought of checking here first before taking this to workshop (if needed). Thanks everyone for reading this and helping me, if you know anything relevant. Cheers.