Examples of hidden loads
Again, it's important to stress that there's never a load fee that's not disclosed, but a prospectus can be very long and dense paperwork, making it hard to know exactly what you're paying for if you aren't prone to that sort of reading. There are only the three types of load fees mentioned above, but the front-end load fee is glaringly obvious since you pay it at the time the fund is opened.
Load fees that might be considered hidden are the level load fee (also known as the 12b-1 fee) and the back-end load fee (aka contingent deferred sales charge). Both are taken directly from the investment's gain throughout the time the investment is active, making it a virtually invisible transaction, especially if the mutual fund is performing well.
It gets increasingly complicated when the back-end load fee is one that decreases over time since you may not be aware of how much it actually is at any given point in your investment. Since it's taken out when your mutual fund is sold, you may not even notice that the money is missing, especially if you've held the mutual fund for many years and don't check it often.