My babies having a hard time starting for the last couple of months, and just today I noticed clicking (knocking mabye?) that varies directly with the rpm's. This is my first car and I'd be suprised if it was knocking due to how quiet it is(but I know very little). It's a little tapping sound, and it sounds like it's coming from just under the intake manifold. After my last warranty oil change I was told I need a Fuel Injector Service or somthing along those lines. Also I've been switching between 87 and 93 octane due to prices. Any sugestions?