Contact Microphone Noise Isolation

I have a piezo contact microphone which I am using to detect running water in a pipe. I intend to use this signal to determine the time at which water turns on or off in the pipe. However, there is noise nearby which drowns out the sound of water flowing. This noise often coincides with the water turning on or off, but is not a sufficient indicator by itself, therefore, I would like to remove the noise.

The microphone is directly attached to the pipe with flowing water. The noise originates about 20 ft away from the microphone. Though the noise source does not make direct contact with the pipe, there are enough interconnects nearby that the noise dominates the sound.

How can I modify my microphone setup – by adding dampening material or changing placement – to reduce the amount of noise picked up by the microphone?