[Diviner]

Symptoms
I have noticed this year (for about a month) that the steering wheel initially makes a single distinct "click" when turned.  [Maybe some people would describe it as a soft "clunk".  Or possibly "knocking"?]
So, regardless of the direction the front tyres happen to be pointing, if I hold the steering wheel stationary there is no click.  If I decide to turn the steering wheel, then I can turn it through perhaps 1 cm (roughly 3°) with no noise, then there is the single click, and then it is silent again as I continue to turn the steering wheel. 

Diagnosis
The sound suggests to me that there could be 'play' in the system (some looseness of fit, resulting in 'slap'), although I can't feel the difference in the steering. 
From a quick look the symptoms that come up online seem to be more to do with repeated clunking noises, so I'm not sure that they have anything to do with what I'm observing. 

Background
Back in mid-January I was parked at 90° at the end of a parking lot.  When I pulled out of the space I turned hard left, not realising I was close to the kerb, and the left front tyre ended up driving over the kerb (cutting the corner).  However, I didn't notice the steering wheel noise during January or February.  For a while I thought the steering might be pulling left, but eventually I decided I was probably misdiagnosing an effect of the typical road camber.... 
Aside from that I'm a fairly careful driver, although occasionally I can't avoid hitting some minor/moderate potholes. 

Questions

• What would most likely cause those symptoms?  (Anything to do with a "knuckle"??)
• Any consequences of the underlying issue?  (Aside from from the irritating noise.)
• How urgently should it be repaired?
• Any rough indication of how much repair might cost?  (Tens, hundreds, or thousands of AUD?)

[Diviner]

A few points of note to distinguish from other online descriptions: 

• it's a single click/clunk, not regular clicking/clunking
• it happens for a small turn of the steering wheel, not requiring a large turn, and specifically not requiring turning from lock to lock
• there is no feeling of wobble in either the car body or steering wheel
• noticeable on ordinary roads (not only bumpy tracks)
• noticeable seemingly irrespective of speed (not tested in detail, and not tested stationary)
• doesn't require "rapid" turning of steering wheel (although perhaps it's more obvious with 'purposeful' turning of the wheel?)

[Aye30]

The dreaded flexible steering coupler, goes something like this - The electric power steering motor sits along side the steering shaft, It is connected to the column via two interlocking metal 4 pronged discs, with the flexible coupler  providing a non metal to metal buffer between the two pronged ends. The whole power assist system is controlled with the help of the SAS Steering Angle Sensor, It detects which direction the wheel is being turned and then provides the steering electric motor with a corresponding  amount of power. The Click heard when the flexible coupler wears down is the electric motor assisting you, to turn  the column in the direction you have chosen, When you turn the wheel back the other direction, you will get another click, as the motor changes direction and it assists you to turn the column the opposite direction. When driving at very slow speed and making 10 degree back and forth changes to the direction, the wheel will feel a small delay before the power assist will kick in.
If this feels similar the flexible coupler is only about $15, however it's about a 3 to 4 hour job to remove the steering column and replace the part, And one member here was charged for the repair and the "mechanic" never performed the service and then disappeared. As for prices, it varies. I've read some older posts quoting prices, and when I rang the same place the price had gone up.

[eye30]

I had something similar.

After checking couplings etc it turned put to be a bush located in the front top suspension mount which had worn so made clicking noise when turning steering wheel.

May have been part number 54612.

[Diviner]

Thanks very much, eye30 and Aye30. 

I drove again yesterday and realised that I had not quite recognised the symptoms fully.  Let me try to clarify in more detail. 

Symptoms
The click seems to happen specifically when the steering wheel is turned through the "neutral" position (12 o'clock, the position for driving straight), although — as I mentioned before — if I hold the steering wheel stationary (at any orientation) there is no click.  If I decide to turn the steering wheel, then (depending on where the wheel was initially) I can turn it with no noise, then there is the single click as the steering wheel passes neutral, and then it is silent again as I continue to turn the steering wheel.   

So, if I turn back and forth between 11 o'clock and 1 o'clock, say, then I get the impression of the click occurring around 12 o'clock, once for each traverse of the steering wheel.  I am not sure whether the click occurs at precisely the same position turning anticlockwise and clockwise, or not.  It seems to be slightly more noticeable when turning right (clockwise), and definitely more noticeable when the turn is firmer (faster rotation of the steering wheel). 
I think there is a minimum amount of turn for the click to be evident:  so if I jiggled the steering wheel just fractionally left and right of neutral, then I wouldn't get a click. 

On the other hand, suppose I am already making a gentle RH turn (wheel at 1 o'clock), then I execute a sharper turn (wheel at 3 o'clock), and return to the gentle RH turn (wheel at 1 o'clock):  then there would be no click, as the steering wheel has not passed through the "neutral" (12 o'clock) position. 

Diagnosis
Before hearing your feedback, I had started to wonder if it was like a single ridge on a gear that had worn down.  Although this is from me picturing a rack-and-pinion style arrangement that probably has more to do with my childhood experience of playing with Lego Technic than anything that actually occurs within an i30! 

Consequences
Supposing that it is either a "bush" (bearing-strut / front shock absorber bearing?) or a "flexible coupler" (I can't seem to find anything to do with power steering for my model on PartSouq.com), is the only consequence the fact that the sound is annoying, or are there any larger concerns?  Safety concerns? 
(If it's really only a slight delay before power assist is activated, then I can't imagine that it's having any practical effect on the steering response.) 

Aside from this issue, I wouldn't have planned to have my next routine service until around the end of 2025.  So would it make sense to wait, or not? 

Mechanics / Workshops
I am pretty happy with my current service centre in Sydney.  I'm certainly not an expert, but they seem to price reasonably, and aren't pushy to do optional extras.  They've been there for years, so I don't think I need to be concerned about them disappearing.... 

I don't have any complaints about the official Hyundai service centres either, it's just that their pricing for regular services was higher (the last time I checked) for my 2010 model.  Also quoted higher than elsewhere for replacement keys.  But I did get pretty good pricing on a new battery from one in Melbourne last year. 

[Aye30]

Hi, the slight delay I mentioned, will only be present when the flexible coupler has worn away to almost nothing. You wont feel it as it is the electric steering motor "catching up" to the prongs in either change of direction. If your click is present with the battery disconnected from the power steering, then it is definitely not the flexible coupler.

[Diviner]

Thanks for the clarification, Aye30. 

Meanwhile, following your mention of power steering, I've just been looking at the pinned thread i30 FD power steering coupler repair in Perth, Australia, which could be related.

[Diviner]

Sorry to revise the description of symptoms, but I had the opportunity to drive in a carpark with more space, and tried turning the steering wheel from lock to lock while driving slowly forward or in reverse.  The clicks (or soft clunks) in that case were not particularly happening at the 12 o'clock position, but earlier on when coming back from the 'lock' position. 
Aside from that, it's generally still as I described before.  It's only evident once when turning the steering wheel in a particular direction (clockwise or anticlockwise), even if there is a pause in turning.  And typically I can turn the steering wheel for a bit without any noise, then there may be a single click, and then no further noise as I continue to turn the steering wheel in the same direction. 
Perhaps the click is heard when the power steering kicks in?  Perhaps this is why it's less/not evident for extremely soft/slow turning?