The send light blinks alot

Well if it works perfect and has no problems then no you don't need a new modem. if it is not doing so well and is messing up a lot then yes i would look into one, Other then that sounds normal for a router or ethernet to be active or none active.

You do got random programs on your pc that do connect to internet while not around or not even using or browsen the net.

Routers send and receive information all the time. If the lights don't blink, then you have a problem. If you get automatic updates from any website or if websites have tickers or changing pictures or advertisements on them, it will flash even more.