My baby had two MRIs by the time he was six weeks old for brain damage he suffered at birth. I was in the room for the second one. It was cold, but they gave us both heated blankets. It was loud as well, even with ear plugs. He was sedated so he slept through most of it, even though it was loud. Basically he just lay on a stretcher in the middle of a white ring. Nothing came near his body. The machine made ticking noises and then would go BRAH BRAH BRAH for a while. TICK TICK TICK BRAH BRAH BRAH. That was all.
Honestly, it was no big deal. The worst part for me was watching them try to find a vein on a six week old for the contrast dye and not being able to feed him beforehand (he was starving!).