The flickering is normal, I guess..
On my ISDN modem the green light flickers too.
If it flickers it means that there are data's running through
your wire. Nothing unusual when you're online

The slow download speed has nothing to do with your flickering, like I said.
Try to download from highspeed connections like DSL, Cable or T3. (You can see the speeds of the hosts in the search window.)
Also prefer to download files which are distributed over the network so you can download from multiple hosts (swarming.)