[Obama_Is_Sabotaging_America]

The witness said the aircraft was just above tree level and both engines sputtering.. Witness said nothing about weather. Sounds like it ran out of fuel to me, or.. Could be contaminated fuel, too.

[Yosemitest]

Contaminated Fuel is possible, but not likely.
I'd really like to knows more about the weather at the time.
I suspect severe weather on final that did damage to the engines, and a micro-burst downdraft.
If there was severe thunderstorms in the area, like lightening and the lack of thunder due to turbulent air, the sound of the engines relative to the witness's position could have been affected.