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