I have read conflicting reports about this IS issue. Before I got my copy, I kept reading posts from people saying it was loud, and posts from people saying they couldn't hear it.
I can't hear mine (unless I put my ear to the lens, really). It's no louder than any other IS I have come across so far.
Maybe there's a variance in manufacturing?
Re: filters. I have never tried the reverse GND. One of these days.
Other than that, I have found myself using filters less and less. The 10-stop ND is about the only thing I use anymore. My Lee kit has been gathering dust. Granted, I haven't been out shooting landscapes much lately, which might explain it, hehe.
Sony A7RII and a bunch of lenses.