As far as headers hissing/ratting goes, I got my TSX with DC headers put on already by the previous owners (also a test pipe, but I added back a Magnaflow high-flow cat because as a motorcyclist/bicyclist as well, I am all for emissions filtering).
They made that "rattling hiss on throttle" sound, which was solved by using a double braided flex pipe instead of the one that the headers came with.
In fact, I believe I came to that solution via posting to this very forum - here it is!
My aftermarket headers (DC Racing) "hiss" on acceleration... What are my options? I got my TSX about 3 years ago, and have always heard this rattling hiss kind of sound when accelerating. I noticed if I accelerate slowly (light on the throttle) it doesn't happen, only if I depress it at least...
www.tsxclub.com
For me, the flex pipe that has worked well are from Vibrant: the
VPE-62606 was initially indicated for use with the stock cat converter (or perhaps, urk, the test pipe...); but to work with the Magnaflow cat converter I have, I eventually had to upsize slightly to the
VPE-62608 to fit better (while the 62606 did work with it to solve the rattle/hiss, it was very tight and stressed a different exhaust gasket that leaked after a while, and everything fit much better with the slightly larger size).