Valve problem?

Hello again everybody, I want to ask what's cause my engine to make like a clattering, knocking sound on the right side? It's a '94 V6 4.3 L S-10 with TBI. I'm thinking it may be my valves because it does it the worst when I use 87 octane fuel. How much are valve jobs btw? Thanks

Probably a lifter, try doing an oil flush and see if it goes away.

Here's a link with the best flush advice
http://www.automotiveforums.com/vbulletin/showthread.php?t=519475