Over the last month Junk bonds have begun to underperform Treasuries:
http://finance.yahoo.com/q/bc?s=HYG&t=1m&l=on&z=l&q=l&c=ief
Many corporations have been abusing their balance sheets in recent years, and will soon have to rollover a mountain of accumulated debt:
http://www.zerohedge.com/news/2014-07-28/chart-has-high-yield-investors-running-hills
This is the Achilles Heel of our current economic paradigm. Diminishing returns on ever more marginal debt: