I've switched from stock to Corsa to Borla stingersto Corsa again and now to Loudmouths (which might be the keepers for my personal tastes). Anyway, what I recommend is: First, make sure the pipe is pushed all the way in. I've found that while trying to adjust the tips with the clamps still loose, the pipes would sometimes start to work their way out before tightening all the way. Next, make sure you have actually tightened them enough. When I've tightened mine to the point where it seems like enough, the pipes would still move in some cases (especially with the heavy Corsa mufflers). Then I checked with the torque wrench, and there was quite a bit more to go until the torque spec.

All the ones I've tried use band clamps (like stock). Corsa says to tighten to 45 ft-lbs. Borla to 32 ft-lbs. SLP didn't give a spec but I used 32 ft-lbs. All worked fine after I tightened to spec.