I did a check and my Brent Mason Treble (pre-TCI, but same multi-tap wiring concept) is definitely noisier than my other humbuckers. I am also guessing it's due to the extra winds on the slug coil. Even though they are grounded in humbucker mode I believe they still factor in.
Many humbuckers are not completely silent, though. The coils have to be exact mirrors of each other, but often times one coil is wound differently from the other for tonal reasons. The only one I have right now that is truly silent is a Wilde/Bill Lawrence. The others (PRS, Duncan, Suhr) all pick up a little noise, but noticeably less than the PRS Brent Mason pickup.