This is alot like the summer of 1998. Back then the market drifted higher day after day with alot of complacency. Then, seemingly out of nowhere, in mid-July the market sold off hard one day and never stopped selling off for a few weeks. In August of that year all the LTCM stuff, Russian ruble crisis, etc, etc hit the market full force.
Right now, underneath the radar (as it has been for about 2-3 years now) are the whispers of FNM and the potential crisis there and for their counter-parties. It's always something to remember that the noise gets louder as the prices decline, the cry for a "reason" becomes more mandatory and it becomes something of a vicious circle.
Perhaps, this might provide the catalyst in the coming weeks.