mblindsey posted this a couple of years ago:
"To record with the MicroTrack II's 1/4” inputs, you must record from a balanced source with TRS balanced cables. If you are recording from an unbalanced line level source or a microphone with an unbalanced (TS) cable, use the 1/8” input instead (with mono microphones, a mono to stereo adapter is recommended); connecting unbalanced cables to the 1/4" TRS inputs yields an audible clicking sound that is recorded. You can change your input source from the MicroTrack II’s Main Menu>Record Settings>Input Source.
If you are recording with a phantom powered condenser microphone, you must use a TRS balanced cable."
Failure to do so can result in the "sprinkler noise" you are describing.