I lubricate my switch springs with Victorinox Multi-Tool oil--haven't heard any pingy sounds since I started doing that. I also line the space under the PCB with some foamy rubber shelf liner for sound absorption. I think I know what you're saying regarding some switches sounding differently, like the spring sticks to the stem and falls off rapidly or something--hard to explain. I've had it happen with MX Blues too. It's a bit time consuming, but it helps to actuate every swtich a few times once you click them into the switch plate to check for uniformity. I discovered a couple of bad Clears that way in my old batch--they had some really smoothed out defective bump feeling (unlubricated even).