I have an 87 longbed Dakota that I bought new. It’s my work truck. Lately it has developed a chirping noise that I hear best with the rear slider window open. I think it is safe to say that it is not coming from under the hood. When I accelerate from a stop the chirping noise increases in pitch and frequency. The frequency does not change when the auto trans up shifts. There has been no noticeable out-of-the-ordinary vibrations, even at freeway speeds. I have stopped driving on the freeway since the chirping became impossible to ignore. The chirping becomes less and less audible the faster I go as the pitch and frequency increases. When just starting from a dead stop, it sounds like a metallic scraping noise. Whenever I take my foot off the gas the chirping stops, even when still coasting, so it only occurs under load. It does not occur when the truck is stopped and the engine is revved. Does anyone have a clue?