Is the power track your using a orange coloured one?, Hornby have a DDC power track specially for DCC.
If it is the Orange coloured Power track socket, then you can take off the cover and remove the Supression Capaictor in that or change it for a DCC power track which is: R8241
Also it could be the Back EMF is set wrong. Had this problem on a few baccy chips recently.
Hope that helps but try the power track solution 1st.
tks
George