Noble Group will hold an investor conference in Singapore today in another bid to fight off attacks over its accounting practices after endorsement from a second auditor failed to convince markets and detractors last week. The beleaguered Hong Kong-based commodities trader said it would present "a comprehensive explanation of how [its] business works" and the findings of a PricewaterhouseCoopers review. Noble, Asia's biggest commodities house by revenue, has been battling a reputational crisis since February, when little-known Iceberg Research started assailing its accounting policies. Others, including Muddy Waters and Hong Kong's GMT Research, followed with similar allegations. In its strongest yet defence, Noble last week released the findings of the PwC review that endorsed its accounting practices. But that failed to appease the market. After a short-lived jump on Tuesday - the day after the report was released - Noble's shares took another dive, falling 21 per cent over the past week to close at S$0.49 (HK$2.70) on Friday. At the heart of the debate was how Noble realised gains from the mark-to-market approach from its long-term physical and derivative commodities contracts. PwC did nothing more than what Ernst & Young, Noble's auditor, had been doing for years, ensuring the compliance with accounting rules, Iceberg said. "The PwC review fails to address the market's concerns. Investors want to know the real value of these [mark-to-market gains], not whether Noble successfully exploits accounting loopholes," Iceberg said. GMT was equally unmoved. "Noble is playing with words whilst avoiding answering the real issues. We've never accused Noble of not following [international financial reporting] standards. Our point is that they are being overly aggressive," GMT founder Gillem Tulloch said told the South China Morning Post . "We think Noble has simply used PwC to validate its past use of aggressive accounting so that it can continue using the same aggressive accounting without giving away any meaningful improvements in disclosure. Houdini would be proud of them." An anaemic commodities market has compounded Noble's woes. After it released weaker earnings and higher debt levels last week, Moody's put Noble's investment grade rating on negative outlook, following a similar action by Standard & Poor's in June.