Basically, when the water heats up you get more suspended material and organisms in the water, and it shows up on the SI units like this. However, it should be equal on both sides.
A few things to check:
Make sure the transducer connector is tight. You may even want to slightly (very gently) bend the pins out just a little to make it snug.
Is the transducer tilted slightly up on the right side? If so, level it out. You may be seeing more suspended material near the surface if the transducer is angled.
Do you have a friend or someone also with a SI unit you can hook your unit up on their boat? It may be the transdcuer itself. If you see the same thing on their setup, then its probably the head unit. If you don't see it, then its the transducer.
If it is the head unit, it may be as simple as reinstalling the firmware/software. You would have to backdate the firmware to a previous version first, the reinstall the current version. Remember to follow all the steps correctly before and after each install.
http://forums.sideimagingsoft.com/index.php?topic=14.0Good Luck, and let me know if that helps.
Robert