Unless the tiller is off that tiny gap in the bow bolt mating surfaces shouldnt hurt a thing. I have owned a number of bow bolt bows and some had that tiny gap at the back when strung and it never causes a noise, at proper BH the limbs stopping on the shot should prevent any movement there.
Speaking from experience with many bows and bowyers I can tell you for certain that "stock" strings on new bows are an afterthought for most bowyers. They are mostly there to get the bow out the door in a shootable condition. Some bowyers do a decent job making the strings themselves others are atrocious, some farm the making out with similar mixed results. There are only a handful of bowyers out there who truly give the string making the attention it deserves or farm it out to someone truly competent. Flemish string making is an art unto itself contrary to what some will say. The string makes the bow, it is like the tires on a car. I think you should strongly consider ditching that stock string for a custom. I can emphatically recommend the following three makers who are my go tos Ten Ring Strings, Mountain Muffler Strings, and RMSGear. Material wise it is largely personal preference but Id recommend against any of the older materials and go with something from the newer gen and not too skinny. Measure your string length in a manner where your string wont end up with too many twists or not enough, both ends of the spectrum can contribute to noise IMO.