Valve Noise RB25DET NEO

[DTT_Eruc]

Good day buddies.... So i have recently installed some Tomei Poncams(Intake 260 9.15 and Exhaust 262 9.15 lift) for my engine (RB25DET NEO).... After they were installed i never checked the shim clearance(p.s shims are above bucket type), due to it being drop in cams and my buddy who installed them never had to re-shim. Unfortunately after i started the car i heard a ticking noise from the back of the head and then investigated the reason of the noise. For a second i taught it was the body oil used(20w50) and i live in the caribbean. So i change the oil to 10w50 and the noise reduce a bit but was still there... When i pop the cam cover and check the clearances this was the results. 

*Exhaust * Numbers are in "thou" reading

1.0.019
2.0.019
3.0.019
4.0.019
5.0.020
6.0.020
7.0.020
8.0.020
9.0.020
10.0.20
11.0.20 + 0.011
12.0.018 tight or 0.017

AS Tomei recommend there clearances to be .018 thou mine reads close to Nissan specs and never did any head work....  but for when i checked the clearance on valve #11 and #12 i notice that was the problem.... What can cause that such big clearance #11 and tight clearance on #12 ....Btw this is a stock head and never done any head work as my goal was to just see how long the engine can last....