Installed about 3 weeks ago as a replacement resonator on my 03' 540i and definitely boosted the sound I wanted over the stock resonator. Before installing I installed a 3" Magnaflow 12219 satin stainless steel center muffler. Now that both items are installed and I've had a few weeks to get used to the new sound, I love it! Sounds deep and hoarse when you're on it, but quiet enough when cruising and no hum This is a good setting if you want to hear the V8 in your E39 540 a bit without being annoying.