Have just purchased my first focus, its a 1.6 auto, and I seem to have developed a squeak, not sure if I have a mouse residing in my car, but sometimes when the auto box changes gear there seems to be a squeak, not sure what it is and already have had a good look around on the forum and cant seem to find any info on it.

It sounds like a belt slipping to me, only lasts a tenth of a second but can get annoying sometimes.

Can anybody point me in the right direction on what could be causing it?