Modem looks like downloading by itself

Soemtimes when i get home from work i will look at my modem and the red lights are flashing just as they do when i am downloading something. I leave all programs off and computer is running when I am gone. Is there anyway to tell if something is downloading or uploading on its own?

Does your modem have wireless turned on? Somebody could be using your WIFI.

Do you have automatic updates turned on?

Is your antivirus updating?

could be many things and it will be a search to find it.

The only thing you could really do is run a packet sniffer like Wireshark and have it record while you are not physically using your computer and then analyze what kind of data is being transmitted.