After reading and researching for many months here and elsewhere, I installed a set of the Magnaflow mufflers #15623. The sound at idle and "goosing" it is great. The notorious resonance on my first long trip between 1600 to 1800 rpm is horrible--I'm near deaf after two days of this. It is bad enough to rattle a lot of items in the car especially when pulling up grades on the highway. These are coming off and I guess back to the stock mufflers. This is on a basically stock LT4 engine and exhaust system. I have other Maganflow products on my son's Nissan Frontier and my brothers S10 pickup that are great. I called and talked to Magnaflow tech support--they are no help. Any other suggestings other than Corsas? Are the Dynomax replacments any better? I will make someone a great deal on these if they want them.