Soffit mesh. Yes, very much like window screen material, but just a hair bigger holes. Mounted the mesh with black wire ties alternated with black zip ties. THe only problem with this combo is that the mesh on the lower part of the airdam is somewhat "loose", so it's not as smooth looking as the gutter guard. But then again, being a lazya$$, I didn't want to take off any of the plastic coverings on the bottom so Soffit mesh is easy to put in. I might attach the Soffit mesh to gutter guard, just to give it something stiff to lay on, then it would look nicer, but who looks down there anyway?
Just to clarify, my 05RX had Michelin MXV4's...and to be fair, the Bridgegstone Alenzas were brand new so that may be the main reason for the quiet ride after replacement. Which Bridgestones do you have?

 

I have Michelin's SP2 on my Carrera, Pirelli on our Boxster and Dunlop 19" on our 2010 RX350. The Dunlops are the most quiet of all. Not to say they are the best handling, but it's an SUV for god's sake. The SP2's are the best handling along with the Pirelli tires.
I have Goodyear "runflats" on our Mini S and they are the hardest riding tires I ever had. But no spare comes with the Mini.
I did not want the dealear to change the tires to Michelin, based on the fact I don't trust the dealer to propoerly balance the tires or scratch the wheels.
My decision