Mine makes a similar noise when revs drop below 900 rpm when the engine is cold on a cold (sub 5c) day.

Cannot be heard once warmed up. My engine has 107k but had a new oil pump at 99k.

 

Have you taken the rocker cover off? Just to check there is nothing loose in there?

I guess you could also try a thicker oil which if that solves it would indicate bearing wear.

 

Have you checked the valve clearances?
Nice to see another ITB setup btw

 

Have you also checked the tensioner pulley / bearings?

 

Going to whip the cover off this weekend and see if I can see owt, I do have some cams to throw in it so will rebuild the head when I do that. If it still knocks then poo...
I may order an oil pump

Flanders - the itb's are fantastic!

 

I can't remember exactly how mine sounded, but it's worth checking these.

 

The Engine in my old S2000 used to make the exact same noise, A lot of people over in the US also used to and still do have the same noise and there are many threads on it.

I found the noise changed if you pulled out the coils one by one, suggesting that it is a piston/bottom end related noise

No one actually knows for sure what it is but the majority think it is Piston Slap as it is only there at Idle. I worried about it for months with my last car and eventually just decided that its not worth worrying anymore. Lots of people said that had they have had the noise for years, but i have never seen any threads say that the noise resulted in any engine failure.

Also out of interest what year is your engine?

Ill try to find some of the threads.

 

Have a read of this: https://www.s2ki.com/s2000/topic/110...age__hl__knock

 

Cheers fella, I will have a read of that thread tonight.
Car's a 99 but had a spoon bottom end put in in 2004.

I think it could be in head as it was first apparent after we re fitted the head a couple of years ago, I had completely forgotten about it till my mate told me last night.