I don't get it. My sound keeps going out when I'm in the aircraft. If I back out of MSFS, to main menu, all sounds are back. Sometimes no sounds when I push fly now. Sometimes I have sound inside, but them it goes out. 

Do you have several sound output devices like speakers and headset?

I've had issues now and then with the sound recently (no sound in cockpit)  but I don't know whether it comes from the sim or some problem  between the last Windows patch and the headset driver.

Check in the sound menu of general options that the proper output is selected.  MSFS tends to deselect it at my end.

Edited January 10, 20233 yr by Dominique_K

I have two sound devices in my PC; the onboard sound (Realtek chip), and an external audio interface (that I use for audio production); a Digidesign Mbox II.     Although the latter is set as my default sound device on my PC, I found that I would get stutters if MSFS was left to "default sound device" in the settings.   So I "hard select" it to the Digidesign unit.

However..... after each MSFS update (large and small), MSFS sets it back to "default" and the stutters return.   So after each update I have to change that setting.

TL;DR - check MSFS's sound device, and if it says "default" change it to your actual sound device.

Edited January 10, 20233 yr by JYW