What do you mean, all the time?
As said in the FAQ, the servers are being pinged. This occures every 40 seconds, if the server is "unreachable", i.e. the ping does not work. You can turn off the pinging by checking the 'My computer is permanently connected to the Internet' box on the 'Updating (Connections)' page of the program settings.
Otherwise, avast does not send anything besides the update requests.
You can also do a search on this forum, this has been discussed a million times here already...
Vlk