The famous acronym, KISS, (Keep It Simple Simon), comes to mind here: my Lionel Classics 2-400E whistle was beginning to sound anemic, and would also initiate an intermittant sound WITHOUT the whistle button being depressed! 
At first, I thought it might be dirty track, but I decided to clean the both the contact rollers and the tender wheels first. Voila! After this cleaning, the whistle sounded MUCH louder and there was no more intermittant self-activation.
Sometimes, the simple solution is the most effective - and easiest! 
