DB: I've definitely noticed stuff. For example, my cavalier when I had Valvoline Maxlife Blend 10W-40 in it over the summer, there was VERY noticeable lifter ticking. Heck, I have a recording of it on youtube if you care to hear it. But I changed it to PP 5W-30, and it is gone, except occasionally when I cold start it is there for a few minutes.
Another example, our 4.6L Expedition had MC 5W-20 in it, and it had a noticeably loud lifter, it was ticking. Got it changed to 76 (ConcoPhilips) 5W-20, and it is gone, and the engine is much quieter. It also runs smoother. On the MC, there was slightly more vibration during acceleration than with the Conventional.
Another example, our 4.6L Expedition had MC 5W-20 in it, and it had a noticeably loud lifter, it was ticking. Got it changed to 76 (ConcoPhilips) 5W-20, and it is gone, and the engine is much quieter. It also runs smoother. On the MC, there was slightly more vibration during acceleration than with the Conventional.