based purely on your description I'd ask the following question:
Were the vocals the loudest thing?
If yes, then it could be that the vocals distorted the input of your preamp/recorder. You'll find more often on cheaper recorders that there are settings which allow the recorder to have an overloaded input and have a lower signal than would clip the ADC (which is why you don't see anything clipping digitally).
If no, then it's likely an over-driven signal chain at the show (an input was too hot, the soundguy pushed the speakers too hard, bad mic, etc).
You won't be able to fix either of these, but one of them is preventable.