with magnaflow system I had lean bank codes every other tank. took off the resonator and installed a glass pack to attempt to kill the drone and instant codes that wood not go away, Then took off the magnaflow and ran just the glass pack and instant constant codes, removed everything and installed Corsa cat back and no code at all, I have stainless headers and 2.5 high flow cat forward cat system as well. Yes I run K&N and ran with no oil to eliminate that possibility, also TB was all cleaned as well. been chasing the code now for a few years.The exhaust was causing the lean bank codes.power same as the magnaflow system at 1/2 the noise in the cab, can still hear easily but not annoying.