The car looks great. I love the yellow, i love the engine bay... grat job. Your dedication shows in the amazing work you did.
A comment on the H pipe is that somewhere i read that the crossover pipe should be of less diameter than the rest. I dont know how that will change anything. But when it comes to vibrations (causes the resonance sound you hear) sometimes small changes can affect the natural resonance of a system. That said it will be difficult to have two systems identical unless the pipes are from a kit. Otherwise there will be some slight differences that change the natural resonance of the system, which probably explains why in some cases it will resonate while not in others.
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