When using elytra and flying, if you change your texture pack and go back into the game without landing, the flying sound stops. It resumes once you stop and start flying again.

Start flying and change texture pack while still in mid-air.
Go back into the game and the flying sound will be gone.
Land and fly again to resume wing sound.

Reproduction steps provided by moesh:

1. Open world and equip elytra and fireworks
2. Fly and use fireworks until "air rushing by" sound loop begins
3. Press F3+T to reload resources
4. Observe issue: "air rushing by" noise will not play until landing and starting again