Ok, if this is a regular occurrence, my thoughts would be that someone in your neighbourhood might have a device connected to the network that shouldn't be connected, or, that he or she is a bandwidth hog. In the case of a device that shouldn't be connected, that device would be transmitting data that would show up as background noise. There might be a distinct difference in noise levels and as a result, a difference in the modem's signal to noise ratio. I'd copy the modem's signal level table, before and after 2 am and paste the data into a document such as MS Word, so that you can compare the data. You should be able to call tech support and ask the tech to look at the historical data. I don't know the timeframe of that data, every minute, every five minutes, etc, etc? In any event, it could show a difference pre to post 2 am.
As for determining the presence of a bandwidth hog on the network, that's a good question. Maybe @RogersAndy might have some ideas and tools available to see the usage overview of all users connected to a particular network card at the neighbourhood node.