If history repeats itself, TA Associates selling is actually very good for the stock price.
MetroPCS stock bottoms at $5.65/share in Nov 2009, when the price went back up to around $9/share in June 2010, TA Associates started its massive selling. During this process, the stock went all the way up to $18, then when the stock came back down to around $16/share at the end of July 2011, TA Associates stoped the selling.
So from when TA Associates started to when it end, between 2010 to 2011, MetroPCS stock price has gained about 80%. Fast forward to September 2012, now TA Associates is unloading again from around the $10/share mark, also during a comeback from $5.53/share in June 2012.
PS: I think TA Associates was one of the original investors back in 2007 who invested millions in MetroPCS and as a result, received about 30 million shares of the company stock.