Yeah its the factory installed decoder Tsunami.
The other day I was running my bachmann Spectrum K4 with sound. I lost control of the locomoitve and couldn't stop it. I turned off the power to the layout and tried to start the locomoitve up again. The locomoitve at first would move but the sound wouldn't respond to any function. Later I tried to use it again and the sound would work but the locomoitve would not move. I took the shell off the tender and put another decoder in the locomoitve and it ran fine. I really dont want to send the locomoitve back to bachmann because I've made changes to it. Thanks for any help or comments you have.