I have a 2003 Explorer with almost 117k. I bought it for short money not in the best of shape, and started doing work to it. Ive had it 6 months now and last problems I have with the car are: A/C compressor squeak once every 30 seconds or 1 minute only when a/c is on obviously (still works should I replace it?), Rattle/ metal on metal (exhaust I think[fix?]), and the one that actually worries me which is the clicking sound. I was told by my mechanic it was most likely the lifters or an individual lifter. Ive read some threads about lifter clicking until engine is warmed up. However my clicking happens even after car is at operating temperature. Also it isn't a constant clicking. The more open the throttle the faster it clicks until I let off the throttle or it up shifts. It generally only happens on acceleration from a stop in lower gears.