I've had my '07 IS 250 in on at least 8 occasions for the numerous noises. I've had the TSIB's done on the center speaker, new dash clips as well as insulating the center stack. The noises are better but far from what I expect from a Lexus.
I just received a shipment from Sutherland Felt in MI who produces and supplies felt to the manufacturers with automotive grade pressure sensative adhesive. I got .35mm, .5mm, 1mm and 2mm thicknesses. They sell it by the yard at a reasonable price, between $10 - $20 per yard by 60".
My plan of attack is to put felt between the plastic pieces that make up the center stack. I've had to do this before in a 2002 Acura TL and when I was done you could head a fly breathe.
Fo owners of a non-nav IS, the loud "POP" from the center seems to be coming from the actual center vents and the visible trim piece.
Lexus should change their tag-line to be: "Lexus, the Pursuit of Mediocrity"