The joint auditors of the Hinduja Group-promoted IndusInd Bank-MP Chitale & Co and MSKA & Associates-have written to the bank's board requesting a forensic audit of the derivatives portfolio, highly placed sources within the bank who are privy to the discussions told ET. Following this request, the board has initiated the process of selecting a top firm for conducting forensic audit, said the sources cited above. The private lender, which has faced a 50%-plus market-value erosion in six months, disclosed on March 10 evening certain discrepancies in its derivatives portfolio.