Insurance Probe Drives Down Stocks  NEW YORK (Reuters) - Top U.S. life insurer MetLife Inc.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MET.N target=/stocks/quickinfo/fullquote"&gt;MET.N&lt;/A&gt; said on Friday it had received several subpoenas from  New York Attorney General Eliot Spitzer, in a sign that a probe  into alleged rigging of bids in exchange for fat fees in the  insurance industry is widening.