Quoting ESPN's Jayson Stark, MLBTradeRumors.com mentioned today that the Houston Astros are "hell-bent" on acquiring a closer.
According to the report, the Astros have inquired after Aroldis Chapman, Ken Giles, Andrew Miller, and Brad Boxberger, as well as several potential free agent possibilities (presumably, names like Tyler Clippard, Wade Davis, Joakim Soria, Jim Johnson, Brad Ziegler, Fernando Rodney, and Joe Nathan would be considered).
To accommodate such a move, Houston's 2015 closer, Luke Gregerson, would be moved to a setup role. As the closer, Gregerson posted thirty-one saves last season, with a 3.10 ERA, 2.86 FIP, and 0.95 WHIP.
In Stark's initial report, he mentions that the Astros haven't shown a willingness yet to part with "the type of high-ceiling prospects it would take to deal for Chapman, Miller, or Giles" (which puts the "hell-bent" part of the article in question.)
The speculation is that the Astros are looking for a high-velocity, high-strikeout reliever to close out games for them.