how about going with the simplest and most plausible explanation.

some people have money stuck on gox, have to pay some bills and were not able to get a large wire out, thus they bought btc on gox, sent it to bitstamp and are dumping so they have some cash to pay their bills.  Or to pay a bill/invoice from a merchant that uses bitstamp or one of the party payment providers that use bitstamp

simple enough?

also look at the macd on the 1 and 3 day charts...