Goldman (GS) shares tumbled 4% Monday as investors ran for cover under the latest barrage of bad news about the banks.

Goldman stock particularly wasn’t helped by a report over the weekend that investigators are looking at possible insider trading allegations tied to the firm’s dealings in transactions including health-care mergers.

Monday’s selloff comes after a two-month-long surge in Goldman’s shares. The company’s stock rose 23% between Aug. 27, the day Fed chief Ben Bernanke said in Jackson Hole, Wyo., that the Fed might expand its support for the economy, and the first week of this month, when the Fed announced the rollout of its latest easing plan.

So to some degree, Goldman shares have simply been rising when riskier assets are in vogue. Today’s selloff comes at a time of various worries coming to a head — notably the news of another probe of Wall Street, but also the Irish bailout and the muni bond mess.

In any case, the now aborted rally brought Goldman shares within 10% of the high they reached in April just before the Securities and Exchange Commission sued the firm for its failure to fully disclose risks to investors in a bubble-era subprime debt deal.

Goldman put those charges to bed by paying $550 million, but its shareholders continue to pay handsomely for the uncertainty surrounding the firm’s various legal exposures.

Goldman isn’t the only bank being hit Monday. The other big standalone investment bank, Morgan Stanley (MS), was down 3%. The  big commercial banks, Bank of America (BAC), JPMorgan Chase (JPM), Citigroup (C) and Wells Fargo (WFC), were down around 1% each.

The selloff comes on the heels of a report from Barclays Capital that the biggest U.S. lenders may need to raise more than $100 billion to satisfy rising regulatory capital requirements

Another sore spot is the mortgage mess. Barron’s reported this weekend that  big banks could fork over $134 billion to repurchase souring mortgages sold to investors.

In one interesting development on that front, a New Jersey suit against Bank of America’s Countrywide suggests the lender systematically failed to pass mortgage notes along to the trustees in charge of mortgage bond portfolios.

If so, the bank could face an even costlier reckoning from the foreclosure fiasco.