On Fri, 13 Apr 2007 09:01:56 -0700, SparkyGuy
Gave us:

Think of it as a single, shorted secondary turn but *outside* the
laminations. Any field that leaks out of the transformer induces a
current into the strap, and it in turn generates a field that fights
the excitation. It should be thick, wide, and well-shorted, which
means well soldered. Copper is best.

John

No need to ground, I presume...

Have you formed the leads going to your project into twisted pair
yet? I guarantee that will reduce injected noise a LOT.