My maxiama is making a terrible harmonic noise from the exhaust. I have replaced everything from the exhaust manifolds to tail pipe. I notice it mostly at lower RPMs 1200 to 1500 so I am asuming it is the new muffler but before I replaced the cat with a Hi flow cat it went away for awhile or was not as loud. My old cat was bad and partialy hallow and the cat pellets where in the old muffler and had shotguned it to pieces internally. That is why I replaced everything because I thought it was the the blown cat that was causing the noise. Also I have taken off the resonator. Right now I am willing to experiment with a new muffler. The one I have is bone stock and willing to upgade to a less restrictive muffler just not to loud due to fact I live in town and go work at 5:00 a:m. Any one else have this problem? I can live with it but would really like to know the cause.