How do I stop my teeth from hitting while talking after Invisalign?

If your teeth are hitting while talking, in could be a sign of insufficient "freeway space." This is measured comparing your biting position (vertical dimension of occlusion VDO) to the rest position of your teeth apart (vertical dimension of rest VDR). The amount of room from occlusion to rest is called the freeway space. If insufficient, your teeth will hit in places and it can be traumatic, especially to your anterior (front) teeth. You should return to your dentist immediately Depending on the severity, he may simply eliminate an interference with minor occlusal (bite) adjustments or you may require additional Invisalign treatment.

When your Invisalign was completed all of your teeth should have been hitting simultaneously. If as you say, one tooth is hitting the other that shows me that your Invisalign treatment was incomplete and that you should return to your Orthodontist for a refinement.