Grinding noise coming from underneath the hood

My 2008 Mitsubishi Lancer has recently started making this intermittent grinding noise (it sounds like a chain being dragged across pavement). It sometimes makes this noise while idling or after hitting an uneven spot in the road. Other times the noise starts up for no apparent reason. This grinding sound persists for a few seconds to perhaps a minute or so and then stops.
When I am sitting in the car it sounds like it is coming from the driver's side wheel/tire area but when I popped the hood the noise sounded as though it was coming from somewhere underneath the hood (though I could not localize exactly where).
The car seems to be working harder to accelerate. It makes a moaning noise when it is accelerating up to about 50mph, after which it seems to have an easier time of it. The rpm doesn't go to any crazy levels (not beyond 3000), but it does seem to get to higher levels more readily than it used to.
The gauges on the dash all look normal - nothing seems to be jumping around, temperature is consistent/normal, no oil/engine light or anything like that. I confess I know very little about cars, but I did check the coolant level and that was in the upper range between the low and high markers.