When I installed Ubuntu 17.10, I noticed that the volume icon in Rhythmbox was gone:
But then I found this picture while wandering on the internet and I thought that maybe I'm the only one who has this problem since no one had brought it up.
So I just removed rhythmbox-plugin-alternative-toolbar
as a workaround solution.
But yesterday, I installed Ubuntu 17.10 for my friend and he had the exact same problem as I did.
So, is there any way for me to retrieve the missing volume icon?
Oh, well, I found the answer myself. It's not a bug, just go into plugin -> alternative toolbar setting, there's un option to turn on volume icon.
Menu -> Preferences -> Plugin, where you can click and highlight alternative toolbar. Now that it is highlighted, at the bottom right there is another Preference, within which you can turn on Volume Control among other things.
When I used your method, the Playback control became weird (I couldn't find how to loop one song).