I've been listening to a lot of Chameleon Circuit (a 'trock' band) and it reminded me that in season 3 of Doctor Who, the Master returns as is hinted over the series with a slight change.
We later find out in the series what that is:
The other Time Lords, don't like being trapped in the time lock, and thus have set up 'the sound of drums' in the master's head so he could, nay, would return and free them.
Has this ever been stated in the original series? Is this an in-universe retcon of the masters previous motives (i.e it fits with the Master of old, but adds an explanation)? Or is it a definite change? I know the Master was a megalomaniac but I don't know how extensive that tendency was for him....did this change things?