Professional investors are starting to worry that stock prices are getting out of hand compared with where they should be. Valuation has been a key concern of late for market participants in a bull market that just passed its eighth anniversary. The S&P 500 now trades at 18.3 times forward earnings — the 12-month period ahead — which marks the highest level since the market turned around after the financial crisis. In the latest Bank of America Merrill Lynch fund manager survey, a net 34 percent of respondents find that equities are overvalued. That’s the highest level in the history of the survey going back 17 years. On top of that, a net 81 percent believe that the U.S. is the “most overvalued region” compared with other areas of the world. “Investor positioning argues for a risk rally pause in March/April, with allocation to equities at a two-year high and bond allocation at a three-year low,” Michael Hartnett, BofAML’s chief investment strategist, said in a statement issued the same day that major averages slid amid a sharp sell-off in bank stocks. The most recent threat identified in some corners of the market is that a disparity between Treasury yields and the S&P 500 dividend yield could threaten stocks. The thinking is that rising government bond yields would divert money away from lower-yielding equities.