I think that Andy is onto it. Increase your squelch slider a little. Your 639 hz noise is at a very low level (<1000) and the 634 hz tone well above 1000 so you should be able to remove the noise. In addition, set all your btonelength parameters to 1.2 or 1.4 and leave the atonelengths at 0.6. This combination of tweaks I bet will fix it.