[Tangent]

It's most likely just normal operation of the fan clutch. When it's hot it engages the clutch and turns the fan faster. The extra load from the fan (not to mention the A/C compressor) will raise the idle a bit. When you accelerate and really get that fan turning you get quite a loud roaring noise. It goes away when you floor it because the higher rpms = higher fan speed = faster air flow through radiator = radiator cools + air flowing trough it doesn't get as hot = fan clutch thermostat cools down and disengages the clutch. There' will be a noticable loss of power because that fan takes a good bit of power to turn. Open the hood when the engine is hot and have somebody rev the engine to ~2000 rpm in park or neutral (with parking brake on for safety). You should be able to easily identify that it's the fan making all the noise.