guys pls help

my bike started making weird noise in a weird situation
when I pedal with power, its fine
when I don't pedal, its fine
but when I pedal without power, so slower than I need to out power in, there's this rough clunking sound and I can also feel it in my pedals too.
I'm pretty sure its coming from my IGH, or at least it comes from the back wheel.
How do I figure it out? is my IGH fucked? Maybe water got in where the speed wire connects, and something started rusting? Its been raining a bunch past month and my bike is always parked outside.

its a SRAM SPECTRO S7
here's videos of the problem
https://files.catbox.moe/o67n4v.mp4
https://files.catbox.moe/7t1cvf.mp4

what could it be? could I service it myself? also I noticed sometimes on the first speed it can skip when I'm putting only a little power.
also I had problem where the chain went off the back sprocket, if I went too fast and dropped off like a sidewalk, so I put the wheel a bit farther back so the chain had more tension, maybe i out the chain back in wrong or something? when its on the sprockets, its kinda a lot tone side and not centered on the teeth.