I have a windows phone game published already in the marketplace.
Here is a link :
I want a background music loop and some music to be played at the homescreen.
Then you are on the righ place. Welcome.
Start searching and downloading.
Do not forget to give proper credit, people who made the sounds.
Freesound is not for music. See http://freesound.org/help/faq/#other-0. Loops that are building blocks for music are allowed though - perhaps that will be enough for your cause.
In addition to the links behind the link above, I can recommend http://jamendo.com and http://opengameart.org . Make sure to read and understand the licenses to respect the terms under which the artists share their work.
I'd love to contribute some music/sound effects to your game? My email in firstname.lastname@example.org if you want to get in touch.
My website is www.joelneale.com but I have a lot more music samples to send over to your email that are not yet online.