Noise after 40 MH

Hi there,

I have a mercury cougar 1999, with 108000 miles, my engine its a V6 2.5 L.

I am having a wierd problem, my engine start making a noise when I go over 40 MH, the noise is like when you run your car without oil, the kind of noise, but I never let the happend, I change the oil every 3K miles, I use 10w-40, and lucas oil, to prevent this kind of problem, I am thinking on the fuel injector, but I dont know, or could be the sparks?

I would like to know yours opiions.

thanks