I have not used the Clean Sweep. I personally believe its greatest effect is convincing installers who don't know how to do this, that they can do this (it ha an auto-adjust feature to reverse the EQ). Personally, I beleive that it's preferable to NOT lose the steering wheel volume controls or the EQ. Have they specifically explained the effects of installing the CS on how the system works now? BTW, who are you talking to?

However, I'm not going to say it has noise. Like many products, I bet that in some cars it works great and in a few cars it has noise. The X5 has a rep with many manufacturer companies of being an electrically noisy car - and I know that the LC6 can sound clean in other cars, but it sure had noise in the X5.

I have seen before-and-after RTA curves, published by JL, and while the response is definitely better, it's not as if it's magically flat as a pancake. The curves aren't easy to tell the vertical dB scale on, either. I'm not certain that the HU output needs equalization - I think that's all in the OEM amp, and if you are adding a volume control, you don't need the OEM amp.

As far as the dash tweeters go, there are basically two schools of tweeter thought. One is silk-dome, low resonant frequency, low crossover point.

The other is harder materials, higher resonant frequency, higher crossover point.

The latter tend to have a peak around 10K, sound "detailed" in the board, but bouncing off of glass, they can easily be found bright and forward and after some time are fatiguing to listen to for may people.

The latter are in my experience based on great-sounding home speaker drivers, where the tweeter and woofer are very close together and you don't have glass surfaces to worry about.

Companies using the first approach include Dynaudio, Morel, DLS, a/d/s/, and to a little lesser degree at times Boston, Alpine X-type, etc.

Companies using the second type include Focal, Diamond, MB Quart, JBL, and Infinity.

Even if you decide that sonically all these sound great in a demo board (something that is a matter of personal opinion), in the X5 door/dash locations, you will have a LOT more musical information up in the windshield if your tweeter plays an octave lower into the upper midrange.

I've been doing this for 18 years. I tried the hard tweeters for a while in my own car a few years back. I found that after a couple years, I was listening to ESPN Radio more than music. I changed my speakers and noticed that I started getting CDs again and started taking them in the car again.

It would have been preferable to spend time sitting in front of my Thiels and my Audio Research and doing nothing but having a drink and listening to a good home music system - but I don't seem to have as much time to do that as I used to. The average American spends 9 hours a week in their car.
As I said above, science has proven that stress ages us, and that music relaxes us. Why miss such an opportunity to improve your surroundings for 9 hours a week?