Noise and some vibration when foot on accelerator (2002 Subaru)

I have a 2002 Outback wagon with about 105K miles. Whenever I engage the accelerator, I hear a loud sound. At first it was metallic, but now it is loud and irregular (not a constant whine. I also notice some vibration at the steering wheel. I also occasionally smell something. We just had it at a Subaru shop and had many costly things flushed and brakes checked. The problem is worse now. As soon as I release the accelerator, the sound ceases. Does anyone know about accelerator-related noise?