Product review (1 stars): Cheaply made - rattles - avoid
I read through the other reviews -- some units really do have compressor units that hum/rattle (because the fan inside rubs up against the casing). Leveling it is important. The one we got has to be tipped forward by 10 to stop the rattling. There's no way to adjust the condenser to stop the rattling either (short of presumably taking the motor/fan assembly apart and rebuilding it).

At $140, it's not worth shipping back; and the repair options aren't so great.