my MacBook Air seems to open up ok but just recently does not make the "start up" sound.

1. Reset SMC by following the directions applicable to your MacBook here ➔ How to Reset SMC. If that does not solve things then-
2. Reset NVRAM/PRAM by following the directions applicable to your MacBook here ➔ How to Reset NVRAM/PRAM. If that does not solve things then-

Axel F.

Sorry Disregard. I am using another macOS. I should have double checked.

You should not be resetting NVRAM every time at boot up because the startup sound should stay there. You are right that it is not a big loss and probably something else that is interfering with that internal setting.

One thing to note that if your sound is muted by you (when you are using your computer) and then you shut it down without unmuting the sound then the start up sound will not sound. Can you double check to see whether that is happening? Thanks.

Axel F.

Before you go, one thing that you should note and that is that when you reset the NVRAM then the sound gets unmuted if it were muted from the previous shut down and that is why you are always successful in hearing the sound after that reset.

Axel F.

Is the sound muted?

Try a PRAM reset (hold the PRAM reset for at least three chimes so it activates several times).

Open System Preferences ➔ Sound ➔ Sound Effects Tab ➔ Play sound on startup : Is that option checked?

Axel F.