Take a look at devices called accelerometers. I know little about them but they might be what you need.
Lots of work has been done in the area of vibration monitoring and the cost for equipment (especially sensors) has dropped in the past 20 yrs though it still may be out of your reach.
You might research publications to understand what frequencies provide the information you need. A microphone, speaker or piezo element (crystal for that matter) might give you the coverage you need though the amplitude may be a problem that requires attention. You'd likely need to filter and amplify the output. It might be that even the smoothest running equipment drives the sensor to full output - got to do some experimenting. Where you go from there has to be determined. Will you just look at RMS values or do you want to digitize the signal for further processing? I would think you could adapt some audio spectrum analysis software but I've no clue if that is too tall an order for a microcontroller.
Not much help but it might give you a little something to work with.