News:
You're not alone. I have been chasing the same thing. Waiting for an order from Roseville with new nuts to tighten down the taillights good and snug and see what happens. I think a lot of mine is tailpipe placement as well. I had them cut just shy of the bumber (under the valence not through).
if the 1/4s have been replaced there may be leaks between the panels [inner & outer ] , tailight seals , floor plugs & trunk seals can be an issue as well
The extensions should stick out of the rear valance about 1/2 inch. If not, the exhaust will drift up under the car and into the trunk. I've seen a lot of muffler shops mount them flush to the valance for looks.