One of my twins has Sensory hypersensitivity and we are taking him 2 times a week to a ocupational Therapy place to help work through it. Kevin also cried all the time as a baby & now as a 5 year old, he still cries when frustrated, angry or gets to overstimulated by noise, people or even messy places. It is something you can learn to control with a baby. Kepping a white noise on is helpful and just holding them tight brings them around quicker sometimes. I know it is hard and you are getting frustrated but imagine that poor childs perceptions of everything. There is quite a bit of literature on the internet.
You have to talk to the parents so they can get the child evaluated. I am not saying that the child has what mine does, it just sounds similar. But any parent would want your input as you see the child everyday & see things they might not. It is important, so just in a calm manner have a discussions of your worries & let them know what you think.
Good Luck
P.S
You could print out a bunch of stuff for them, so they do not feel overwhelmed about researching it & blow off your attempt at help.