A major function of oil is to keep moving parts from contacting each other and wearing. Young engines have clean, close fitting parts that glide easily on thin layers of oil, very little metal-to-metal contact. Old engines have larger and more irregular gaps, harder for the oil to keep the parts from touching and wearing. Thicker oil is ok for older engines, I've changed my last seven cars over to M1 15W50 at 100k, no problems at over 200k. And no deserts here either. Synthetic oil is better at cushioning impacts, and older engines with more play benefit from that. A ticking sound is probably some sort of impact, my VWs and Audis have had ticking valve trains from birth.
One problem often cited with changing to synthetic is that it cleans out congealed oil, sometimes opening up leaks. It's possible it cleaned out some deposits under your piston rings or on your cylinder walls and now there's room for the piston to wobble a bit at the bottom of it's stroke.