I have been using one for a while and I have noticed that if you have not adjusted it properly (i.e. the proper distance from the string) you will have excessive slap, and in some cases some tuning issues. Unfortunately, I have also found that the "correct" distance is not always the same. Sometimes it will be right upon the string at rest, others it could be 1/8th of and inch of the string. A good starting point is to adjust it so you can slide a dollar bill between the string and stopper without touching either. Then you can fine tune it by shooting from their.

Once adjusted it will reduce the felt vibration and while there may be a dull thud it should decrease the noise as well. Also, I have never had a problem tuning my bow once the STS was properly adjusted.