I've had bought the doug thorley long tube headers with the y-pipe for my

silverado i install it with corsa sport cat-back and the problem is that my car

started to sound like noisy echo special in mid rpm , what do u think guys

would it be because the non cat y-pipe or the cat-back

 

its the non cat y-pipe most likely,,,throw a resonator in the y-pipe like a dynomax bullet