Metallic clanking noise in 1999 chevy silverado?

I have a noise that has so far proven unfindable. In idle you hear a metallic clanking noise sort of like a fan blade occasionally hitting a metal shroud, sort of like a clink clink. As you accelerate it seems to increase with rpm, at speed it returns to the same type of noise at idle an occasional clink. If you are at an incline it is greater even at idle. If I put the truck in reverse and accelerate then brake rather harshly it makes the noise in the greatest frequency. It is not the , it is not the torque converter, it is not the flywheel, all of these are brand new, yet the noise continues. Nothing at all is affected by the problem that I can tell, been driving with it for over a year, but it is getting louder and is very annoying.......any ideas..thanks...