Knocking inside? (IS300h)

[Gerr28]

Hello all,
I have an IS300H F-sport (2015) and I love this car, but 2 problems are just appeared which was rare, but now it's occasional and I'm looking for some answers-experiences.
(I also have been in Lexus service, and had a Full service package as well, to find whatever is causing this issue, I directly asked them to check the suspension and etc, but they told me, everything is fine, and the couldn't find any issue, even my brakes are 60% okay, so the don't have to change anything there.)
So my problem is:
When I'm on the road, it is totally fine, silent and smooth. But when I'm turning the car to left or right on a bumpy road specially with low speed (5mph/ 8-10kmh), I can hear a flat knocking from front and rear also inside the car. Not always, but occasionally.
The 2nd: When the situation is the same as I wrote above on the bumpy road and I'm using the brake, I can hear also some "crunching" noise, like somebody is scrubbing 2 spring against each other.
1 Day I asked my partner to sit behind me, let's see how the car is acting, and the mentioned symptoms are gone for 80% so I couldn't hear any knocking or etc.
(The car is left handed)
Do you have any thoughts or did you ever hear experience a situation like that? 
Thanks in advance,
(If there is a post about this, please share it with me, I couldn't check the full history for this. :) )

[Hadrian]

Sounds like a possible broken spring, but you say that it's been checked by Lexus.

[Gerr28]

I had a thought, but they said, everything is fine and cool... 😕