Tell the guy with the compactor to pop the top and check the condition of the power nuts that pull the ram up and down. It sounds like he has a problem with the drive system, even from down below where the chain drive is looped around the pulleys. With the top off, the action of the ram can be observed.
Also, check the continuity of the switches, especially the reversing switch and the top limit switch mounted in the top of the ram chute. If the reversing switch is somehow shorted, it can power both directions of the motor at once, making for a real loud noise briefly. The diagram is under the top & some of the newer ones have a tech sheet in the control panel area, but in case his does not, the tech sheet is here:Tech Sheet for Compactor