After reading this thread, I decided to check all my spokes. The "ping" method didn't work too well as they varied in pitch even if tight, so I took a wrench and checked all of them on my lift. I found at least 3 per wheel that needed to be slightly torqued to match the rest. I would think it's something that everyone should do maybe once a year to be safe. It might add 10 minutes to your yearly check list and I wouldn't count on a service dealer doing it on a yearly service.
