Depending on your actual floorplan, you may need to drop the underside cover closer to the kitchen area to get an eyeball on any leak in that area. Some other thoughts are a plumbing leak under the sink, dripping onto the bottom of the cabinet. Maybe a loose faucet connection or drainpipe. Do you hear it dripping only after flowing water, flushing the toilet, icemaker (if equipped) running? Is the sound constant or intermittent? Has it rained heavily recently? Isolating exactly where the drip is hitting a surface may help. From there, you may be able to follow it to it's source.