98 Volvo S70 Ticking lifters

Could be an oil pressure problem or the camshaft itself

You could have an internal oil leak in the engine which is causing you to lose oil pressure. When you start hearing the noise, pull the oil dipstick out while the car is running. If the oil has a lot of bubbles or looks really foamy then the internal oil leak will be from the oil pick up tube seals. The oil pan will need to be removed to replace the seals. Usually what I see is that a seal gets so bad it just disappears so you would need to clean out the screen as well. I would recommend you take it in to a shop familiar with Volvo to do this repair. I have seen people attempt this repair and miss the missing seal that they still have oil pressure problems and start throwing oil pumps and switches. The worse part is I have seen people use regular $5 dollar tube of silicone for the oil pan when they should be using the chemical gasket from Volvo. So someone that is familiar with the vehicle will know how important it is to clean the oil pan and block mating surface for this repair. So that is where I would start to look in the dipstick. Good luck to you and let us know what you find?

Yep that's how it starts, did you try changing the oil to a heavier weight?