Mutual fund investors can't catch a break these days. Not only have they suffered through three straight years of equity fund declines, but now they're being charged more for the right to do so.

A new study from the U.S. General Accounting Office reveals that the average management expense for the average stock fund has increased from 0.63% to 0.7% of the fund's assets over the last two years. In other words, the fund skims an extra $70 off the top of every $100,000 investment over the course of the year. That's salt in the open wounds of poor market returns.

What's worse -- these fees don't include day-to-day portfolio trading costs. Given the market volatility and the fact that funds are selling off assets to cope with waves of redemptions, the burn of the churn stings.

How could this happen? It's simple, really. Many mutual fund companies have tiered management fees. As the fund asset base grows, management fees decline based on the total asset value. Capital gains and inflows of new money, in theory, help lower the fund's expense ratio. But when net asset values plunge and folks pull out what's left of their money, expense ratios inch higher.

Sometimes, it's more than just inches. At Frontier Equity, the costliest fund in the Morningstar database, annual expenses have risen to a staggering 32%. Tack on an 8% front-end load for the privilege of having your money squandered this way, and it's no wonder the fund's assets have shriveled to a paltry $50,000.

While this is an extreme case, many stock mutual fund investments have raised expenses since you first bought in. Read the latest fund prospectus, which details what your managed money is costing you. And check out the Fool's Mutual Fund Center for more advice and information.

In this market, you don't want to add insult to injury.