[wiredfool]

To be a little more specific, you're conflating two things here.

1) Stress relieving is tensioning the spokes by grabbing pairs and squeezing them. This takes a elastic bending moment in the j-bend and over-stresses it into plastic deformation, permanently changing the shape of the spoke. When relaxed from the stress relieving, the spoke is bent differently, and the stress in the spoke is more uniform with less of a bending moment. (bending moments lead to a compressive stress on one side and tension on the other, superimposed over the tension of the spoke. If the compressive side of the spoke winds up with an actual stress reversal on every wheel revolution, it will start to crack and fail in O(1e6) cycles, or 2000km). Due to the overstress here, this also beds the spoke into the hub.

2) Windup comes from the spoke being a long torsional spring. There's friction between the spoke threads and the nipple, and if the threads aren't lubricated, the friction is enough to twist the spoke instead of tightening the thread. You'll still see some of this with thinner spokes and higher tension, but you can back off a bit on each adjustment and make sure that the spoke isn't twisted before going on. This windup causes the pinging when a new wheel is used for the first time, and each spoke is somewhat unloaded when it's at the bottom of the rotation. This reduces the friction in the threads, and the spoke springs back, changing it's total length.

Incidentally, the highest compression in the rim and highest tension ever in the spokes is in the stress relieving step of wheel building. This is where a super tensioned wheel will potato chip buckle if it's going to. Adding a tire and air pressure reduces the spoke tension. When riding, the bottom ~4ish spokes detension somewhat (depends on the spoke count, numbers are for old school 32ish/ 700c not terribly deep rims).

[jimnotgym]

I wasn't conflating two things, it appears my stress relieval procedure has more steps than yours. For your part 2 (in addition to what you said for part 1) I also used to grab the wheel with one side against my belly, forarms across the rim edge, so elbows at 3 and 9 oclock and hands at 12. Then I would push my elbows down to get the pinging sound you described, and then rotate a quarter turn and repeat. Then turn over and do the same. When it stopped I would retrue the wheel and do it again. If you don't do this you get the pinging you described on your first ride and a therefore a wonky wheel.

I believe this is one of the important steps in making a wheel stay true and not need trueing after one ride. This is described better in the Art of Wheelbuilding if you want to try it.

[jacquesm]

All good stuff this, thank you! Some of it I knew intuitively but not good enough to really understand, let alone explain it to others.

The tire and air pressure thing is perfectly logical and anybody can demonstrate this, as you pump up the tire the spoke pitch goes down.