This seems odd, when I've done it it's more of a scratchy tone - though it does restart and beep a couple of times.
There's nothing you need do while it updates - put it outside if it won't scare the cows ;)
The best way to tell if it's done is check the tiny LED on the front of the gimbal, it alternates red/green while the update is going on - when done it is solid green.

The worst thing you can do is interfere part way through even if it takes up to an hour.
Check the SD card in a computer afterwards, and there is a text file saying success (or not) to confirm.
If it does fail try to download again in case it somehow glitched the copy.
A common issue is the computer adding additional numbers due to similar files being already in the download folder.
You can simply rename without the [1] and it may work, or download again to be sure. 
The file you put on the card should end .bin - and place it directly into the screen you see when you open the SD card like a folder.
- Not in any of the other folders which might be there.
It's advisable to use a card which has been freshly formatted in the camera  to load the firmware.