Hi, the transformers are new stock from my local electronics shop,
they have three types like this, and call them "transformers for decoupling",
and quote primary impedance, and nothing else. I was sure to grab spares.

One, I think was dodgy from the start, and should be replaced,
I can hear the PWM (even though very quiet) through one of the transformers.
I can even hear SOUND and DTMFOUT through that transformer.

It's not just for the neons.. I got the software relay switch working too so far:



It is possible to drive either side of a neon.
With either two transformers per channel,
or, I think, one transformer, and more MOSFETS,
you could move the light from side to side within one neon.