727 upgrade question

I upgraded my 727, the first time and only time last week. I went fishing today powered it up and I was in about 8 foot of water and it read 300 feet.I turned it off and on several times but each time it came up reading the 300 feet. I have the transducer on the trolling motor , which is where it was before with no problems. The only setup difference , I also am running a 898 si off the front. the transducers are about 18 inches apart. Would this cause the erratic reading on the 727?

If not any suggestions

The 898 could be causing sonar interference since they both use the same 200kHz frequency. Try turning it off and see if that stops the problem or not. If it does try setting the Noise Filter menu to a higher setting than it is now (or turn it on if it is not set yet).