Just say "No". (Well, assuming that you're talking about a photography website and not a band's site.)
1. It's just one more thing to load, which can slow down browsing.
2. Some people browse while having their own music play in the background. A competing tune from your website is usually discordant and right off the bat leaves the viewer with a bad impression.
3. If the viewer doesn't have their own music going, they may not be aware of the volume setting on their computer and can get blasted when your music starts unexpectedly - again, bad first impression.
4. Even on sites that allow the viewer to pause or mute the site's music, there is no standardization on where to find these controls, and much of the time they are hidden until you mouse over the proper area. Now the viewer has spent the first X-amount of time looking to shut off the music rather than looking at the site's real content.
5. Go ahead, try to pick music that appeals to every viewer (or at least the vast majority of them). With music tastes so varied, you're more likely to annoy the viewer or have an indifferent reaction, so why add it?
And finally...
6. For a photography site, you ideally want your images to impress on their own merits. Music can do one of two things when paired with an image or slideshow - it can detract from the image, or it can lead to the suspicion that you feel the image needs the music to add something (even if this is not the case).
Just the opinion of someone who does his fair share of web surfing...