You say there it has an eMotion L driving decoder, do you know what sound module it has and how it is connected? If the sound module (say an eMotion S) connects directly to the track then there may be a fight in responding to CV reads from both decoders.
If it is a LGB factory sound (not sure if these ever had any) could the whistle and sounds be triggered with a FA1 signal (the A1 output of the decoder goes to the sound board and the sound board plays specific sounds based upon the number of changes in the output). Try triggering FA1 several times in succession quite quickly. You may need to set the Fast Serial Pulse Chain option in the configuration of the L decoder if this is the case.
If it is a LGB factory sound (not sure if these ever had any) could the whistle and sounds be triggered with a FA1 signal (the A1 output of the decoder goes to the sound board and the sound board plays specific sounds based upon the number of changes in the output). Try triggering FA1 several times in succession quite quickly. You may need to set the Fast Serial Pulse Chain option in the configuration of the L decoder if this is the case.