Magnetic contact microphone from Radio Shack audio transformer

[Dogue]

While experimenting, I accidentally discovered that a Radio Shack audio transformer (1K Ohm primary / 8 Ohm secondary) (http://www.radioshack.com/product/in...ductId=2103254) magnetically attached to a rare earth magnet makes for an interesting contact microphone.

I presume this is because the coil is microphonic. This did not work with several Japanese audio transformers I had of the same specifications.

In initial testing I found that the mic sounds particularly good when the magnet is attached to a larger piece of metal and objects are placed on this larger piece of metal and struck/excited.

This brings me to my question:

is there a way to use such a setup (audio transformer+magnet, attached to piece of larger metal, on which various small objects are mounted) while effectively grounding the mic and minimizing noise/interference?