right, breasts means (I think) that you'll go in backwards, ie lying down head first. So yes, it will be noisy, but it is just the magnets whizzing around the tube, making the image (science bit over!).
You'll be lying down normally, so will be comfy, and you'll be able to see out of the 'tube', as you look down your body. Probably you'll be able to see the medical staff, and they will likely be in a booth. You'll possibly be given instructions like breath now, hold your breath for a count of 2 etc - this is just to get the pics that are needed. It also means that you wont feel alone, as you can see them, AND you can hear them. And they can see you so they'd know if you were in difficulty, and get you out asap.
Top tip? Other than the relaxy advice posted, and your being honest with the staff there re your nerves... If you have cold feet, wear socks.
It will all be fine, honest. It's a loud but totally non-invasive way of getting the images they need. Hope it all goes well, and hope you get a positive outcome from scan.