Thor Industries ( THO) has launched an internal investigation into certain accounting issues at its Dutchmen Manufacturing subsidiary and has voluntarily informed the Securities and Exchange Commission of the probe.The company's audit committee, along with independent outside advisors, are looking into the subsidiary's inventory, accounts receivable, accounts payable and cost of goods sold. Based on preliminary findings, Thor estimates that these issues could result in a reduction to income before taxes of roughly $25 million, or about $16 million in net income. The R.V. and bus manufacturer said it may be required to restate its financial statements for fiscal years 2004 through 2006 and the first quarter of 2007. Shares of Thor were trading down $3.25, or 7.2%, at $41.92.