Alvin: a "clickety click" under acceleration", "sorta like a diesel" sounds too much like knock to be ignored. All the wrong sounds for lifters or valves. All the right conditions for knock. It may be normal (mine does it a little), or you may have a mixture or carbon build-up problem. Grant p.s.: since from your post you've been to your mechanic, i think the main thing broken is your mechanic.