That is what they do when they are on DCC. There is nothing you can do and you should not leave a DC engine on a DCC track when not in use. The DCC system puts about 14V AC to the rails at all times. The DC engine is picking up this 14V and it is going right to the motor. This causes the motor to vibrate at the freq of the DCC system, and since current is passing through the motor the motor is generating heat.
A DC engine can run on DCC tracks do to a feature called 0 streaching. What happens is the DCC command station sends a long packet of 0s down one of the rails. This packet of 0s changes the potential between the rails for a few microseconds which is enough time to cause the DC motor to move. The frequency of the packets and the rail they are send down is what changes the direction and speed of a DC loco on DCC tracks.
A Veteran, whether active duty, retired, national guard, or reserve, is someone who, at one point in his or her life, wrote a blank check made payable to "The United States of America" for an amount of "up to and including my life."
Owner of the South Massey Railway.