usefulnoise

@usefulnoise
@ShadowDance
Maybe this is interesting for you: As I had the same issue but did not wanna mess around too much and some where successful with 3rd party sata cables, I was looking for a way to get this done w/o loosing the HDD slides into the SATA slot option.
I found this (hope this does not count as advertisement):
https://www.aliexpress.com/item/1005002595620272.html
which seems to be the general harness of a Lenovo X3100 M5 Server. I was also looking to get some screw-able SATA mounts, but could not find any that would not require me doing the cable works and soldering too.
However the Lenovo cables looked promising and as it turns out, you just use this as a drop in replacement. The screws fit. However you have to mount them from the front side instead the back, but the case has enough space to do that.

 
You do however need to push very hard, to get the screws to grip, but even the threads match.
I did a bit of grinding on the metal frame though to reduce the tension on the plastic of the connector cause it is a bit thicker. Not sure that is required though (I think not).
For the fifth slot some grinding will be inevitable though. Since that slot is not populated for me right now (and has to wait a bit on current pricing unless I find a bargain) and one cable set has 4 cables, this was no issue. Another two cable sets are on the way though (have another Helios64).
I do not know how you cut the connectors of the original harness to get power only, but I used a separation disk on a Dremel like tool. Worked like a charm.
The cables are all similar length so you need to do try a bit until you find a position that works and does not twist the cable too much but gets it to the ports on the board.
Here what I ended up with (sorry for the sub-optimal quality but only saw this now on the PC and I do not want to disassemble the case again)

 
Hope that is helpful for anyone. I am super happy with this solution
I have not had any issues with my ZFS setup anymore since.
 
Cheers
 

@usefulnoise I'd start by trying all different suggestions in this thread, e.g. limiting speed, disabling ncq, if you're not using raw disks (i.e. partitions or dm-crypt), make sure you've disabled io schedulers on the disks, etc.
 
Example: libata.force=3.0G,noncq,noncqtrim
 
Disabling ncqtrim is probably unnecessary, but doesn't give any benefit with spinning disks anyway.
 
If none of this helps, and you're sure the disks aren't actually faulty, I'd recommend trying the SATA controller firmware update (it didn't help me) or possibly experimenting with removing noise. Hook the PSU to a grounded wall socket, use 3rd party SATA cables, or try rerouting them.
 
Possibly, if you're desperate, try removing the metal clips from the SATA cables (the clip that hooks into the motherboard socket), it shouldn't be a problem, but could perhaps function as an antenna for noise.