I have a little chaintug on the end of my driveside dropout (forkend, whatever). I use it, and after 15 mins or so of fiddling around with my chain tension and wheel alignment, I can get it to a nice sweet spot where the chain doesn't bind and there is no slack when I go from forward pedaling to back pedaling.

Afterwards however, when I take it out for a ride, the chain starts making painful noises, and then the slack returns. What do you all think is happening? How to fix it? Is it possible to find that sweet spot and remain there indefinately, or is some slack inevitable? Do I need a better chainring (I'm currently using a stronglight)? Or will it be fixed by centering the chainring on the spider somehow? Or maybe the chain is somehow to blame? Maybe I just need to torque the axle nuts harder? Thoughts?