Question about Arlo VMS3230 set of 2

By "no sound" is it meant that sound wants to be heard from the video image (Arlo Cam)?
Probably because these cameras do not have a micro.

https://www.arlo.com/de...

Otherwise use IPCams that also have a (built-in) microphone.
There are also IPCams to which you can connect external microphones / speakers (for 2-way audio).