You're not talking about the "sparkiness" of the machine? I don't have much emi but this thing makes a ton of noise. It's a shock coming from a CTX.
If a machine is "making noise," I'd first start by thinking "EMI" -- whether I think there's EMI present, or not.
I am sure you know the following, but for the benefit of those who don't...
If you stand still, hold your coil stationary, and you are hearing chatter, it is almost surely EMI (unless you have a short in your coil cable, or a loose connection of your coil cable to your control box, or something like that).
Meanwhile, if your machine is quiet/stable when holding the coil still, but you get chatter when sweeping the ground,
and you don't believe it is actual metal in the ground, your ground balance is likely off.
Finally, if your machine is quiet/stable when holding your coil stationary, but there is iron in the ground, and the machine is "chattering" due to iron falses, the propensity for falsing can be lowered via LIMITS SETTINGS (increase the amount of screen that is "grayed out"), sensitivity settings (adjust lower), proper ground balance, and target recovery speed (adjust higher).
The machine SHOULD be stable (aside from being swept over metal in the ground), and can be MADE stable with proper noise cancel, ground balance, and then sensitivity adjustment down to the level where whatever remaining EMI (that could not be "noise-cancelled") is made to be barely audible by your sensitivity setting...
Steve