So today I tried to put the bungs into my KEF q350, it is immediately clear to me that the bung is way too small for the rear port, it could slip right in!
Update: Found an old bung which was inside the left side speaker, and managed to remove it with a kitchen tong. Can't find the bung for the right side speaker.
Are there any effect to sound with having a bung loose inside the cabinet.
Highly unlikely. Not saying that it won't, but if your not getting any weird differences between the two speakers then your good to go. Have a good root around if it bothers you.