Went today insted. Changed diff fluid... Bolts were so badly overtightened D:

And it are the sway bar links indeed, completely shot. Gonna change them along with the sway bar bushings. Any recomendation for budget decent ones?

I'd check out RockAuto and you can get both for like 40 bucks.

installed Moog endlinks, noise is gone and car handles noticeably better. Thanks for the advises

Hey FuriousVegan,
I've been having a similar sound on my G35.
What exactly did you do or replace to get rid of that thumping rear sound?

I replaced the Sweaybar Endlinks, lift the car up and try wiggling them, there should be no olay in them at all. My were moving around like crazy. Also check the sway bar bushings for ware too!