As junk bonds plunge in value, many investors are wonderingwhy.

There's no obvious explanation for the 1.5 percent decline inU.S. high-yield securities in the past month, or the $9.9 billionof cash pulled from mutual funds that buy the debt. The most likelyreason is that investors are increasingly uncomfortable hangingonto bonds that are expensive by historical measures.

Chalk this one up to a collective bout of angst that looks quitedifferent from the 3.2 percent drop in speculative-grade bonds inMay and June of last year. That rout was triggered by the prospectof less Federal Reserve stimulus and, while a withdrawal ofeasy-money policies still weighs on investors' minds, that's notthe full story now.