I have a video of it. I just uploaded it for you.
The noise is at 0:05.
It was more noticeable in real life than in the video. Passengers would be surprised when they hear the noise. It would happen over speed bumps, irregularities on the roar, or just small changes of road height on the highway.
I spent almost 400 bucks going to different shops trying to fix that noise (adjusting settings, adding some rubber paddings, trying to fix the angle of the height adjuster etc.). I came to the conclusion that the way the rear piece for height adjustment doesn't match the Stinger. They probably reused a piece designed for another car that just seemed to fit.
Here is the email I wrote to KW and they never answered:
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Hello,
I drive a Kia Stinger and I am using your v3 coilovers.
I am experiencing a loud clunking sound in the rear right suspension. It seems to occur whenever I go over a hole/gap or after a bump, when the wheel comes back up after dropping. I had my mechanic have a look at the setup and his guess is that the part with the perch (height adjuster?) attached to the spring is coming loose when the wheel is dropping and then when it comes up, it does reattach but with a slight angle. So the noise comes from that part that keeps tilting between straight and angled everytime I run over a bump. I did not have this problem when my car was lower but I had to raise it for clearance reasons (by around 0.5cm). Do you have any tips for fixing this? or some advice in case this is due to an improper setup.
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If it wasn't for that annoying noise, I would have kept them because they were otherwise perfect. (comfort, stability, handling etc.) Some other people experienced the same problem, so I do not believe in the faulty part possibility. The ride height adjuster is just not shaped as it should be.