All joking aside, I'm a bit puzzled as well by so many who can't actually hear what the plug is doing. I mean it's subtle no doubt about it. But it is altering the signal. In fact, if you turn both dials all the way up and still can't hear it working...you might want to get your hearing checked. Although, at least in my testing, turning both dials all the way up was pretty unpleasantly distorted...unless that's what you're after.
PS: What's happened to the forum?? We're back to showing edits that were made to posts only seconds after they've been posted AND you're no longer taken to the last post...now we're back to being taken to your own last post. Sheesh.