This all started in the weeks following an oil change back in the fall. I never noticed the noise, a friend did, and then it preceded to get more and more noticeable. I thought this had to do with the oil filter they put it, so I did an oil change and used a volvo filter, with no change.

The ticking appears to be coming from the head, specifically, cylinder number 2. If I unplug the injector for that cylinder, it goes away entirely. It only makes the noise under load, so if I rev it up, the noise isn't there as the RPMs are dropping.

Here's a video, from a cold start. The noise starts occurring around 2 minutes in. It really doesn't do it much when cold. Could this be the oil sump o rings going bad?

Volvo s60 2.4t motor ticking - YouTube

 

I would start by doing a compression test to se the diference between the other ones. Try using and additive into the engine like Seafoam in the oil through the oil cap and some lucas oil treatment.

 

well fuel injectors make a rhythmic click and the volvo ones are especially noticeable but im not thinking thats what the problem is.
it sounds like the coil pack arching and shorting out. check out your #2 coil and spark plug, swap it out with #4 or 5 do the same thing with the fuel injector if you swap out your spark plug, coil, and injector to #5 and the problem also swaps there's your answer. (im a fan of free diagnosing lol, why throw parts at a problem)