Not sure, I've had two S5's now and neither did this.
It's possible some random setting that carried over for most of us etc.
I know the first S5 when it restored my old phone settings the screen timeout was set for 45 seconds for example, well that's not a valid option so it made the menu look funky lol. The second one it didn't do that as I had changed to 30 seconds before exchanging again.
I imagine something similar, some setting carried over to disable the sound and we just dunno which/where.
I did a lot of traveling yesterday and bounced on and off 3G and 4G and no data many times, no sounds.
Maybe it's the roaming guards too glitching? I do disable those too.