Maybe nothing to do with your noise but my Focus made an irritating (quite loud) noise from the rear which increased and decreased according the speed I was doing. I thought it might be a wheel bearing. I put up with this for ages and eventually was told by my garage that it was possibly because the tyres were worn unevenly. You can check this by running your hand over the tread in each direction. After several emails to Pirelli and Ford, neither answered but I eventually managed to speak to someone at Pirelli who told me it was a common problem with Focusses because they have four wheel tracking. I changed all four tyres and had the tracking done which solved it. Annoying thing was I think the car had left the factory like that and if I had acted earlier could have had it done under warranty.