USAGE: What do you call this sound?

When you put your tonge on the inside of your lower lip and do a click.
It's a really cool sound, but there doesn't seem to be a description for
it.

It's part of an (evil) language I'm designing.  For instance, |katén|
and |katín| are both pronounced as [t`in].  As opposed, of course, to
|katún|, which is naturally pronounced [qOtan].