There are perhaps 200 posts discussing this subject within the top pinned thread but since information still trickles in every week from multiple forums I'll summarize the situation as I know it today.
The motor noise was determined to be tail-bearing outer race spin and lubricant failure by YouTube channel
Auto Repair Videos. I also spent time looking at the bearing selection just a few days ago and found that there is one deficiency regarding the bearing size chosen, essentially that it's too large for the light loading conditions present in the tail-end position. The exceptional YouTube mechanic making the videos mentioned above has also rebuilt several Kona/Niro GRUs and those have never required more than replacement bearings as the gears remain undamaged, leaving us with the important clues that the GRU noise is due to the bearings and
not the gears.
I've personally been studying the GRU failures for more than 2 years and the evidence shows that the internal factory magnet is not working as it should to
permanently sequester the copious steel particles normally shed off machine-hobbed gear teeth during break-in. The result of that contamination is damage to the ball and roller bearings which reduces their useful lifetime. But it's still a matter of chance as to if any particular Kona develops an audible noise as a result within the expected vehicle lifetime.
My theory is that this happens because Hyundai/Mobis did not restrain the internal magnet securely but rather left it loose in a pocket to rattle around.
Steel particles will only stick to a magnet when they are fresh and during driving will find that magnet (just by chance) within minutes. But if they are subjected to any sort of mechanical working that attraction is much reduced. While stuck to the moving magnet, captured particles wear against a rib at one side of the aluminium pocket until their magnetic attraction becomes too low to keep them in place. When they return to circulation that's when repeated ingestion by the bearings does the damage to the raceways. The oil shows very small non-magnetic black particles and high PPM levels of iron.
Video images of the magnet in my own Kona show it to be relatively clean despite the car covering 27,000 km. It should in fact have a significant loading of particles held in place for the life of the EV. I take that as evidence of the inefficacy of the magnet regarding its intended function. That is a huge problem as the gearbox relies on that working properly.
The reason your oil is as you described is because all of the above processes have completed. The vast majority of
first oil change reports are the same once past approx 10,000 km, including my own 2019 at 19,000 km (11,800 miles). Oil changes at much lower kms (see Ozkona's
photo at 1,000 km) show the process in mid-stream with both visible particles and blackened oil present. The reason for the blackness is not confirmed but the high volume of aluminium found in nearly all used-oil lab analyses is a prime suspect, noting that there are
no normal aluminium wear surfaces present in the GRU.
Specific to your Kona, I have to mention that we have vetted the two recommended magnetic drain plugs on the basis that gearbox applications have an important requirement - that the magnet has zero chance of breaking off inside the GRU. Most plugs are designed for engines and automatics where damage is unlikely should that happen. The Nissan Leaf uses a protruding magnet similar to the Dorman part and it may be just fine. But, in both that application and the Kona, the oil flow is violent near the drain and fill openings and a magnet protruding into that space will be subject to a dynamic loading situation, just like a chimney in a high wind. This is not the case in an engine or automatic transmission as the plug is located in the oil sump. If that magnet breaks off your Kona will suffer a catastrophic drivetrain failure. I'd be remiss as an engineer to not highly recommend that you change this as soon as possible to either the Votex or Toyota parts that are short and remain out of the oil flow. The risk may be low but you need to know that it's not zero.
As for buying the car at end of lease, although the GRU bearing damage has been done the chance of a noise problem from the GRU is actually very low. I think the 2023 is very unlikely to have a motor noise because the newer motor part numbers indicate that Hyundai found a problem early on. If you have the (unique to USA) 10 year warranty you've really got nothing to worry about.
Reference videos:
