I'm a Dummy, Tell Me About Turntable Mats

That is why the Origin Live Mat works so well. This is an engineered material with different characteristics at the record/mat than mat/platter. The goals are to avoid reflecting vibration back up into the LP, to absorb/dissipate them in the material, and to do all this uniformly across the full range of frequency and dynamics. Simply felt or rubber mats just aren't up to the task. The best they can do is make a few areas better at the cost of making some other areas worse. In other words like Ralph says they will not be neutral.

@astolfor PM me. I have an unused SPH Cu mat.

Thank you atmasphere, I think you said it better than I. 
Lew, I know of no hard data that says it is a definitive sonic problem. We both know it exists because we hear it directly. If we hear it the assumption would be the stylus does also. I apologize if I contradicted myself. But it is useful to define our terms so we all know what we are talking about. Record noise is what you hear in the background behind the music including dirt and scratches. Let us say that tracking noise is the noise generated directly by the stylus tracking the record which in all respects is just like that diaphragm in the Victrola. The mat has to dampen the resonance without reflecting it back. IMHO the record has to be held down tightly as the mat is not doing it's job if the record is partially in the air. I think the fact that disabling the vacuum increases tracking noise is telling. You use the Sota reflex clamp which performs the same function as long as you are using that washer over the spindle. Keep your amp off and listen to the tracking noise with and without the clamp. See if you get the same results I did. 

I think this is like what the Supreme Court justice said about pornography. To paraphrase, he said he couldn’t define it but he knew it when he saw it. I can’t define tracking noise but I know it when I hear it. Except I’m not even sure of that.