In the Sample window, play a sample whose loop is defined. While the sample is playing, advance the sample start point in small increments (repeat this at least 6 to 8 times to see the error). Now press the Undo button at half-second intervals. You'll hear Loop's voice playing exponentially.
This may cause some errors (crash, memory-leaks, etc.).
When I encountered this error, what I did was try some loop points on the sample. Yeah, I did some unusual processing on the sample because it didn't have a usual frequency. I was trying to find good loop points in the "Rain" sound sample.