OK
Many hours of testing including eliminating all Lionel engines, caboses, and lighted end unit tank car. I tried changing the DCS chanels as suggested, with no difference.
BUT I discovered something I had not realized before and I may have led us all astray. My appologies. I have the problem elswhere. It happens when the train crosses a break from one DCS channel to another. The horn will either not sound, or continue to sound for several feet even though the button has been released.
Any thought??