It would be good if you could test the torrents in your local area network while it's cut off from the internet - so it would be just you. If you can, try running a torrent server and "downloading" something trough torrent off another machine, and see if it still causes trouble. If yes, then it's something in your own network, but if no, then it's probably caused by something outside your network - I could well imagine it's your ISP.
They advertise here too that any file sharing traffic detected causes the connection to be scaled down to a dialup speed (otherwise it's at least 10Mbps) for some time, and if the use continues, the time is extended. Sort of like punishing; they know, and admit, that legal data is transferred too - like Linux setup disc images, for example - but according to them the amount of illegal data transferred is so big that it's their only chance or something. On the other hand that feels like they're just trying to cure a disease after it took on, but not care about where it came (and comes again), thus making it all for no good; on the other hand I understand it's one of the rare ways to actually spare bandwith for the non file transfer things.