Found the source of the annoying hum!

[Toad]

I was having trouble with an annoying hum in certain edits in T1, which didn't seem to occur in T2. This evening I started getting the same problem in T2 (in tracks which didn't have SIR or Ambience plugged in)and finally discovered the source. It's coming from the input devices. Purely by accident, I moved one of them back from the side of the offending track so that the arrow disappeared - and so did the noise. I've tried it several times on several offending tracks, and it looks like that's the solution.
Don't know if that goes down as a bug or just something that might be worthwhile putting in the manual next time.
Thanks to everyone for your inputs.

[ceenda]

Glad to hear you got it sorted!

If it's a Mic-in, you might want to check for proximity to power cables to find the source of the hum.