This is just a theory, but I've been around business long enough to know the antics that are played. I believe there's two possible scenarios.
Scenario 1: A company, someone like Pandora, doesn't want the competition and is behind the shorting - making it difficult for STTK to get financing on decent terms.
Scenario 2: Someone/ some company wants to buy STTK on the cheap... same outcome as scenario 1, shorting the Hell out of the stock to keep the price down prior to the acquisition.
AMIO,