I've got a 2001 Kia Sportage, 4cyl., 2.0 liter, RWD with 132,000 miles. I hear a sort of grinding/rattling noise when I drive uphill. If I take my foot off the accelerator the noise stops. I've done a lot of driving in mountains, where I've had to put the car in first or second gear to slow it going downhill. I'm not sure if it's a transmission-related noise, a fuel pump or even valves rattling.
I've taken it to two mechanics, who failed to diagnose it.