this can happen if you have a lot of connections and transfers going on, or if many files are being prepared for sharing the first time--especially on startup.

Just be patient with the hashing time--it should only happen once. Here are more ways to manage bandwidth regularly:

To cut down on the number of connections, clear the inactive downloads and then go to Library->Incomplete and delete the 0KB files (they all try to connect on startup).

To limit the bandwidth used for uploads look at the settings in the preferences. setting it at ~80% leaves lots for other services like mail and browsing.