I've just installed a new Eagle Fishelite 480. This unit replaced a Lowrance X125. I did not reuse the Lowrance transducer due to differences in the console plug.
The Eagle works great, both GPS and Sonar.

Every now and then, I'll get a return at 8ft that repeats about every two seconds. This will continue for a few minutes. It looks like a flat oval repeating. I don't see any degradation in other returns. It happens with and without the motor running and at any bottom depth. It will completely disappear for a while and then return.

Has anyone seen this sort of behavior before or have an idea what is happening? Some sort of harmonic?