Miker13,
When you are using any AUTO function the sounder is highly dependent on the digital readout. If you don't have a solid digital depth the sounder will start cycling through the ranges. Turbulence is the most likely cause. The way to find out is to set the sounder into a manual range and then look for gaps in the bottom when going different speeds. Turbulence will usually show up first on 50Khz and then on 200Khz. If you don't see gaps you can try resetting the Bottom Level Setting to -20.
Snips