I have not had the noise, but have previously owned cars with NOISEY diffs (the GT3 for one). This is a "normal" noise. Most diffs with higher lock-ups will make some noise, its the nature of the beast.
I am with Radiation Joe on this one. I would not add a modifier to reduce the noise. IMHO, you are retarding the effectiveness of the clutches....and thus, the overall performance thereof. Personally, I would live with the noise.
Now, for people that are basically city drivers that do not track, etc., it is really a moot point as you wont notice a reduction in lock-up in most cases. So, if that is the case, and you dont like the noise, go ahead and add it. Either way, the diff will still be under warranty.
Tim (apparently likes "3" cars)
E90 M3 -- Current ride
2004 GT3 -- Sold
1997 M3/4 -- Sold
1995 M3 -- Sold