If those seeds are all on slow connections, that could do it. Also, some ISP's throttle connection speeds for torrents to try to discourage people from participating in software and video piracy.
I am NOT accusing you of this, I know a number of totally legit reasons to use torrents. However, this is how the ISP's sometimes look at it.
Some countries have laws against that sort of behavior on the part of an ISP (The ISP is charging for a service after all), but the US has not really approached the issue seriously yet. Odds are when they do we won't like the results anyway. :/