I just purchased a 1998 v70 with 152000 miles. The previous owner said the timing belt was changed 15000 miles ago aling with cam seals and the oil pump. The car made a clicking sound when I test started it on the test drive. The sound always went away within 5 sec someone told me it was the hydraulic lifters. I changed the engine oil and filter using the recomended oil (5w 30 synthetic). I noticed the sound was louder and longer in duration. Today when my wife drove it the sound worsened and I had it towed to my house. The noise sounds like a knock and the oil light comes on and off along with the service light. Do I need all new lifters?

 

The oil pick up tube o-ring or oil pan o-rings might be bad.

But if it is knocking and not tapping now it might be to late.