There are VERY few times when such a thing is a good idea. So few in fact, that you may as well say it's NEVER a good idea.
One of two things is likely to happen with some sort of background track. Either it has to be kept at such a low volume as to allow you to be heard clearly over it, that most people will simply tune it out, or it will become a distraction from the content of your presentation.
It's generally a bad idea to include any sort of sounds in a presentation at all. They end up detracting from the overall experience, and people tend to think in the back of their minds about why you need so many gimmicks, can't your presentation stand on its own merits. If you're going to include any sounds, they should be set up so that you have to click on something to initiate them, so you can work something into the presentation about it. It gives people a chance to prepare, rather than just ambushing them with it.