It's hard to know what this noise is like from your description. When you're turning left, is the noise repetitive or intermittent? How loud is it and can you feel anything to go along with the "knocking" sound?
I've had a "knock" sound come from my RF as I back out of my driveway and over the gutter as I turn the wheel: my wife asked, "What was that?" It was quite loud, and you could feel it as if the suspension bound and then released: it doesn't happen every time and seems specific to a particular set of positional conditions. I consider it "normal", as in, every car is going to have quirks that make different noises. Those that we can live with are not repetitive and annoying: and certainly do not manifest any performance or safety detriments.
When you toss in the different levels of noise sensitivity, some people are hypersensitive to any noise or vibration: even if what bugs them is an artifact of "normal operation".
If you've been in seven times, and the service manager said that Kia may judge it "normal", I guess I'm trying to help prepare you for that (that, "it could be in the glovebox", is beyond the pale condescending behavior, though). But if you really are certain that the level of "knocking", and the frequency of it, is completely not normal, it doesn't matter what anybody else's opinion is, since it is your ride and you have to accept how it is. There are forum members who have complained here and to Kia about similar issues resulting in them ditching the Stinger in the end. Hopefully that isn't you!