How can I disable the auto-play feature when MTP device is connected?

This is probably a better solution (and more likely to work):

1. Open up the file manager (nautilus)
2. Click Edit -> Preferences
3. Click the 'Media' Tab
4. Next to 'Music Player', select 'Do Nothing' from the drop down list.

The media player should still automount and be available from the 'Places' menu. You will still be able to use Rhythmbox to play/manage the device but you will have to open it up manually.

For Ubuntu and specifically the Zorin Ubuntu derivative: Go to system settings>details, click on details, then click on "removable media", then click the check box "never prompt or start programs on media insertion". This is the easiest way to suppress auto-play via the gui. I suppose there is a way to do this via terminal as well, but my post is for those like me that are more comfortable using the gnome gui instead of terminal.

For Zune HD, I found "Do Nothing" for "Music Player" (in Preferences for nautilus) was insufficient. I unchecked "Browse media when inserted" and that seemed to solve the problem, allowing me to charge my Zune HD via my Ubuntu laptop USB port without having the thing freeze up, reboot, etc. (Before that, I had tried "Do Nothing" for "Photos" and "Software", but those didn't solve the problem.)

With this solution, I assume it'll be necessary to manually mount CDs and the like when I insert/connect them.

One possible solution:

1. In Rhythmbox, go to Edit -> Plugins.

2. Untick 'Portable Players - MTP'.

I'm not sure if this will work and it will probably mean that you have to manually enable the plugin if you want to listen to the device.