Not the loudest, but the humming of my microscope lamp, which is a circle-shaped fluorescent light. The humming came from the body of the microscope. I rested the mic on the body of the microscope and did noise reduction and amplified the audio.
A wet plopping sound, such as meat falling into a puddle. I needed the sound of a body dropping into a pool of it's own blood. This was created by letting a soaked rag drop onto several sponges full of water from a height of about a foot.