What would cause a home AC to make a loud house-vibrating noise like a diesel truck when it kicks on?

Hi: Sounds like your internal compressor mounting springs have broken or broken loose and your internal motor is having at it at full bang on start up! Sounds awful don't it!!!!!,,,,, if not that then look at your fan motor supports/belts/bracketry/& such. Equally as offensive when terrible clatter comes in to play. Hope this helps: Jimiwane