I've been following this with interest, because I had no idea what the answer might be when I first read the question. The advice to sand or widen a nock is a good one, to find out if that solves the problem. If it does, then go slow on sanding many more nocks, because the serving will naturally thin out as it is used. Probably after a couple of hundred arrows, the sound will start coming back to normal. Of course, if the serving is really tight, you may have to reserve with thinner serving. I use a 3 under grip, so I like my nocks a little tighter than a split-finger shooter might. On a new string, my nocks will go on the string with a noticeable snap, but they aren't hard to put on or pull off the string.