Steering noise

[fdarre]

Hi i have a c class w204 2008, these six months starting doing a strange noise like hrssss hrsss when turning the steering to the left hand side only, when parking or turning the steering from the same spot. I went to the mechanic and he changed the oil of the power steering and the noise nearly stopped, now these two days it starting to do it again. The mechanic told me that its a faulty valve or the pipes of the oil are too narrow. Don't know but i don't like this noise any help please? Sorry if this thread has been posted as I'm new on this site thanks.