My 2002 impreza has approximately 75,000 miles. Today it started to make a noise when accelerating. I don't know how to describe this noise--it's not a knocking,ticking or rumbling noise, and I'm not sure what a whirring noise is--to me it sounded like a suction of a vacuum cleaner. When I pressed on the gas pedal the noise got louder--but here's the thing it would stop and come back, so it wasn't continually making the noise. In addition I thought I heard a very quiet noise when not accelerating, but not sure--couldn't pinpoint that in traffic. I'm bringing it in for repair on Friday but was wondering if anyone could suggest what might be the problem. I would like to be somewhat knowledgeable about this situation when I speak to the mechanic.