After 4500 miles from new, a whining noise gradually developed in my 09 V70 when rpm were over 1500. The power steering pump was changed, and the fliud of couse, and all was well until the noise returned after about 2000miles. The system was fushed and the "hidden" mesh filter in the base of the fluid reservoir (recently brought to light apparently in a volvo service bulletin) was thouroghly cleaned. All has been well for another 1100 miles but ..........the whinig noise has returned!

Any ideas what could be causing this? Perhaps it might be contamination of the fuid due to deteriorating rubber pipes - but would not expect this in a car of this age.