*** valve help ***

I own a 1999 Mits mirage 1.5, and every so often i hear vlave knock (usually lasts a couple of minutes???) this vehicle has about 145,000 miles on it and i have never adjusted the valves nor can i find the specs to adjust them --- i know how, as long as there is not something funky about them! can anyone give valve specs or insght on what i should do! Thanks for any help you guys/gals can give!

'99 factory manual here.....
http://www.mirage-performance.com/tech/Manuals/Mirage%20Service%20Manuals/99%20Service%20manual/

FWIW
YMMV

Thanks for the manual!!! i should be able to figure everything out on the vehicle with this!!! Thanks again