you tell us. what are you doing? what media sharing do you have setup? does your nexus sync pics with facebook, google+, etc? do you stream music or listen to music you've loaded to the nexus? have you recently installed any new apps, or removed old ones? have you changed any settings?
we can't tell you what exactly is happening. we can only hope to point at something and go "that's likely it". reboot into safe mode and check it again. safe mode doesn't delete anything, it just doesn't load/access any 3rd party apps. if you're still having a problem in safe mode, you'll likely need to wipe the nexus.
1. Press the Power button on your device.
2. Touch & hold the Power off option in the dialog box.
3. Touch OK in the following dialog to start safe mode.
to exit safe mode, restart normally.