I've had an MRI with contrast a few years back, like cleancowgirl said, the noise is pretty much what I found to be the worst part because it sounds like a banging, clacking, drilling and very loud noise. A lot of MRI facilities have "open MRI machines" where it isn't as claustrophobic, there is more space between the tables and some doctor's will order, perhaps ask. A lot of MRI facilities will give you a blanket, a call bell on your lap if you have a question or need to talk to the tech, you just squeeze it and there is a microphone where they can talk to you while you are in the machine. They may talk to you while you are in the machine and ask if you are doing okay. I would call the MRI facility with any questions, but you may be able to listen to relaxing music, ask them if you want to do that, they will most likely give you headphones and remember to not wear any metal the day of the MRI because the MRI machine has magnetic fields in the machine. The tech will ask you at least once probably if you have any metal on because that is very important to not wear metal.
I definitely encourage you to ask your doc's office or the MRI facility any questions. They are there to help you. If you have concerns regarding the IV, maybe tell them that and some facilities may have an IV Team, nurses who are skilled in starting the IV more than others.