How to get rid of the click in a dynamically loading buffer?

I'm sure there is a very simple solution to this out there somewhere, but I can't figure it out myself... I am making a synth that uses an expr object to fill a buffer~ object and playing it back with a groove~. It works pretty well, but there is always a bunch of clicks that I just can't get rid of. Somehow I need create a linear transition between the sample that is currently being written into the buffer, and the samples just after it. Any ideas on how to do this? Any help is very much appreciated.