On tonight's 30 Rock, the writing crew—while trying to solve a debate—inadvertently discovered that Jack appeared to be the voice of www.pronouncify.com. But how did this happen? Thankfully, as the episode went on, we found out. Videos inside.
Here's the aforementioned "discovery" scene:
After that happened, Liz went up to Jack's office and attempted to find out if it really was his voice on the web site:
Aha! So, Jack had done some voice work in college, and—consequently—had popped up randomly (in many places) ever since.
Later, the writing staff had some fun with Jack...
...before again pretending to be Jack and having even more fun with Pete: