Hydraulic lifters are simple devices but they get sticky due to an accumulation of internal varnish. They will then leak down when the engine is off and will tick for a couple of seconds on startup as they refill with oil.

The path of least resistance is to try an Auto-Rx treatment. Auto-Rx should dissolve the varnish and restore the lifters to normal function.

Also, use a synthetic 5W-30 oil.

 

The thinner oil will flow faster when it's cold and fill up the lifters sooner. If you are running a Fram oil filter it's a good idea to go with a different (better) brand. I used to run Fram and I had this problem and found other Volvo owners who blamed the Fram's they were running. I switched to Bosch, noise gone. Others on here like the "Mann", some are Wix believers but Fram is the only one I've seen people having problems with.

 

They will have problems with a lot of them sooner or later. The problem is that it's a slow death. It can take 100,000 miles or 150,000 miles. The thing about that is, many of these cars are already at that mileage. I'm starting to think that filters not designed for these cars can cause all kinds of head issues with their start-up oil starvation. Damaged lifters, bad valve stem seals, and maybe even burnt valves.