Below is a quote from a Web forum member. It sounds plausible, and I
take it as very good news to K-Thunk sufferers!

"My K-thunk is gone...... Today was probably my 6th trip to the dealer
about the K-thunk. Hyundai told them to install a rubber bushing on
top of both rear strut mounts. It worked. I no longer get the sound
that reminded me of a shock that had gone bad. All it took was two
rubber bushing and 1/2 hour labor to make me a happy man. Other than
the K-thunk my LX had been a very satisfactory auto. Those of you who
still have this problem, keep going back, it can be corrected."

Take it with a grain of salt, as this is the only clear-cut case I
have seen where the dealer implemented a fix that was successful.

This is the only real complaint I have with my 06 Sonata. It was very
timely for me, because I have an appointment tomorrow morning (Fri) to
solve the K-Thunk. I will report back tomorrow afternoon. Fingers
crossed!
-

Bob