MTH Double Sounding Soft Keys Fix

Dave, I've been working that issue for some time, on a very low priority basis.  It appeared suddenly a few years ago on a  layout some 10+years after DCS was installed.  I have no idea of what I may have done on the layout at that time.  It seems to end if I turn off my 2nd TIU.  Do you have 2 TIUs?

I had bulbs on the TIU outputs and it made no difference.  Using a Rev L or a Rev G, or anything in between, makes no difference.  Chokes on the inputs (to see if somehow signals were going back to the transformers and then to other TIU) made no difference, nor did having TIU#2 on a separate transformer.

Discussions with MTH led to interim conclusion that POSSIBLY somehow the signal is being inducted/radiated, possibly by two feeds close together, causing another command to issue from the other TIU.    Some of my locos seem more prone to doubletoot than others. 

Only one TIU. I don't know if this could make any difference for you, but I was using track "lock-ons" with allegator clips that have 12 inch leads. So maybe the bulb may need that small gap from the TIU. I should also add the leads wires are 22 gauge.

22 gauge is definitely too small for O-gauge use, so maybe the increased resistance attenuates the second signal????

The 22 gauge is the 12 inch leads going to the bulb off of the TIU post. 14 gauge going to the tracks.