Let me start by saying "crap, never act upon the OCD of others, a blemish once uncovered can't be ignored"....
What I'm feeling is: When there is centering force acting upon the wheel and I turn the wheel offcenter to around 40 degrees, it will give a clunk. If I rotate back to center and then the same direction again, no clunk. If I return to center and then the other direction it will clunk. This happens in Windows but also in game if you drive along and weave at sufficient speed to have enough centering force. So you could state that it's something in the shaft or the belt mechanism which reseats itself fractionally the first time you turn the wheel offcenter in a particular direction.
Same result with both the stock T300RS and GTE rims. I tightened the hexagonal hub screws, no improvement.
Edit: I applied one layer of not particularly thick tape, didn't make any difference. Two layers of tape didn't fit, too tight. I'm more and more convinced the sound is coming from different spots in the wheelbase when turning left and right, so it's some kind of belt mechanism thing.
And now I'm going to ignore it and get back to iRacing