How do I fix this blending of Roblox sound and my sound when walking on a material?

I've made a script whereby it will change the sound of the player's footsteps if the player steps onto a particular material. I've managed to change the player's footstep sound using a touched event and it works very well, however, I did the same, using a touch ended event when the player stops touching the material whereby when testing, it makes it such that both the default Roblox walking sound and my walking sound merge together.

Also, I tested it without the touch ended event and it doesn't merge the sounds. Here's some code: (The code that mixes the Roblox default sound and my sound together)

script.Parent.TouchEnded:connect(function(touchersbody)
    if touchersbody.Parent.Humanoid ~= nil then
        touchersbody.Parent.Head.Running.PlaybackSpeed = 1.85
        touchersbody.Parent.Head.Running.SoundId = "rbxasset://sounds/action_footsteps_plastic.mp3"

    end