So, I have a question.  Is the toner also a Klein?  The reason I ask, is I've had many "fox and hounds" in my day.

Sometimes, I'd find myself with a mismatch on a jobsite...Say a Klein toner and a different manufacturers wand.  When using it like that, the tone would be exactly as you describe.  Weak, crackling, etc.

When properly matched by manufacturer, the tone was always loud and clear.

Don't ask me why, that's above my paygrade.