I am experiencing some strange behavior from my 2008 Ford Escape LTD. At low rpm's, usually when I am going uphill, the engine sounds like a diesel at low throttle and low rpm. It sounds fine at idle, but as soon as I apply light throttle I hear the characteristics rattle of a diesel engine. The engine returns to normal once I get above 30-40 mph or so.

My escape is at 99k miles (bought at 89k) and I'm not sure what maintenance was has bee done on it (sparkplugs, timing belt, etc?). I am fairly mechanically inclined so I would like to investigate things for myself before I bring it into the shop for them to charge $100/hr to not find anything wrong with it.

Does anyone have any suggestions?

(I do have an OBDII reader)

 

Sounds like pre-ignition to me. Could be bad gas, old plugs.
If you're going up the hill and press the throttle hard enough to downshift and get the rpms up high does it go away or continue to do it?