They ALL will sound like that when you replace the OEM headers. You will have to add a large resonator to curb that.
The OEM header has the pre-cat. You take that out and the back pressure drops way more that just replacing the s-pipe. Alot of people (me included) run the DC Spors header. It is a 4-1 design with a rather small collector. This is a major rice maker. My HKS Power with custom 2.5" exhaust was so loud with one 12" resonator, I had to have Jotech add another just to make it bearable on the highway. BTW I have no pre-cat, cat, or OE resonator.
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