I notice lately Norton keeps popping up notices or ads I have low memory left in the mbs but when I check my hard drives I have many gigabits left in memory. Getting sick and tired of Norton continuously trying to ask me to spend more money on their products I don't want. Before they sold out most of these products were already installed on Norton several years ago but now it seems the greed machine has taken over and piecing out features that used to be umbrella-ed in older versions. Just sayin.
You do not say it but I assume you are using the latest version of Norton 360. If not let us know.
If you are then you may find the Settings: Admin Settings: Silent Mode Settings options of use. There is a help section which explains what they do and the following is an image of what my options currently look like.
You can turn "Silent Mode" on manually but only for a set period of up to one day. However if the "Full Screen Detection" is on then silent mode should be automatically engaged when you have anything (e.g. a movie) in full screen mode.
Does that help? If not say in what way it does not and I or others will try again.