Grand Jury Probes AIG, S P Cuts Marsh  NEW YORK (Reuters) - The storm over the U.S. insurance  industry took a new turn Thursday when American International  Group Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=AIG.N target=/stocks/quickinfo/fullquote"&gt;AIG.N&lt;/A&gt; said a federal grand jury is investigating  products it sold that companies might have used to massage  earnings.