On three of my controllers, whenever I press the triggers down, it sounds as if the trigger is coming into contact with a sticky substance and they prying off of it. I don't know if it's the spring or something else, but the sound it makes is extremely annoying to hear. Typically, I wouldn't worry about it because I could just return them for another controller, but that was my mindset for the past three controllers I've purchased and each one is producing the same annoying sound from the triggers.
Any idea as to what this sound could be caused from?