That's what Ken Fisher used to say. You have electrons flowing and now you just placed a cage of ground potential around it confusing the electrons...at least that's was Ken's take on it!!
I've discussed tube shields many years ago and how I prefer Marshall style amps without the tube shields. Many members here felt I was crazy hearing and feeling the difference. Doug Roccaforte commented that there are differences as well. It's nice to see other hearing the same thing.