Hi,
there are two ways to deal with that clipping sound:
1. If the damage is already there, do a little Fade-in /out at the clip. You can do that by using the smart tool (star) and grab the clip at the upper. You will see a little fade icon... Move it to the right until the wave starts at the zero-flatline. At the end of the clip, it is the same procedure, just go left.
2. In the preferences you can choose between splitting clips directly at the position you choose OR tell SONAR, that it do the cut at the next "zero-crossing" I can't tell you the exact naming of the fields, because I have a localized version. It should be something like "Alignment" and "Patter/Raster arrange".
Nevertheless, the reason is, that you split the clip at a position where the level does not equals null. As a result, you have a very fast attack - a crack. You can see it, if you magnify the beginning/end of the clip.