For those interested, I performed a variant of the famous "Golf Tee Mod" on my '05 X3 3.0i this week. I wanted better tones from my exhaust, but didn't want to spend the $$$ for an after-market exhaust system. This is a free mod, and it is very popular on other BMW forums (e90, etc.).
I read many iterations of this mod and settled on zip-ties to cinch the vacuum hose near the exhaust muffler. I gathered a bit of slack in the hose, cinched it air-tight, and zipped two (2) zip-ties over the hose, and tucked the hose safely away from harm and out of sight. Done. Took maybe five minutes total. The result is two, always-open exhaust end-tips and a noticeably DEEPER RUMBLE at low-to-mid RPM's--I am very happy with the results. From what I read and observe, this mod throws no codes, and there is no visual sign of modification; also, I figure the zip-ties are easy to remove if needs be.
Google "Golf Tee Mod" to read (and hear!) how other BMW owners improved their exhaust tone.
