On the Humminbird website there are a couple of suggestions for interference from Minn Kota TMs. One is a mod to the TM, one is tying the ground side of the trolling batteries to the ground side of the crank battery using a fused link. I'm having interference from my Motor Guide TM, going to try the battery connections first. My bow mount 858c is getting interference and I'm running it off of one of the TM batteries.
"Choke" is the generic name of an inductor. This is a passive electronic device that has a really high impedance or rejection characteristic for frequencies above DC. Basically, its a coil of wire usually wrapped around a core material. The wire has to be able to carry the current draw of the depth finder.. which is pretty small really. They are effective if the interference is being transmitted to your DF via the power connection.