It will likely be a sinewave, that is a sinewave with one or more frequencys at various amplitudes and phases.
The exact make up will depend on where you are measuring. It could be a structural resonance excited by the rotating / vibrating component of the machine or it could be a result of bearings on the machine.
You might have some mains interference in there due to mains pick up and possibly some pick up from an electronic speed controller etc.
If there is a mechanical component which is hitting something then you might see a spike of some form due to the contact.
Any of the sample programs that generate a main signal and add noise should suffice nicely to start with. My particular favorite for this type of thing is the 'Signal Generation and Processing.vi' example as its easy to modify and see the effects of what's happening. But there are lots of others in the samples you could consider as well.