Christopher
Using the remote have you tried to hold the bell and whistle buttons at the same time and turn the throttle knob clockwise or counterclockwise. This is supposed to adjust the volume up and down. I would not have the locomotive linked to the app while you do this. Once you find a good middle sound with the remote you like go back to the app and see if the volume will adjust up and down to a level you want. Seemed like I had to do this with a Lionchief Berkshire awhile back from a polar express set and it worked. Some say the app overrides the remote settings but in this case I would at least try it. Seemed like it worked for me.
Brad
