It might be something electrical, the buzzing of lights and other things that are plugged in makes me tick

I would suggest noise-cancelling headphones like another person in the comments, but something else I'd suggest is a different form of entertainment. I don't know you and I don't know how you raise your little one, but I'd really suggest limiting her screentime as well. (That seems to be the big thing for parents right now, at least in public- if you don't, great for you but I still have to say it!) When I was little, I often had visual overstimulation along with auditory overstimulation, and electronic devices are great at both kinds - after all, the games are meant to keep you playing so they get as much revenue as they can. I'd steer her more towards coloring and playing with physical toys for now, especially drawing / coloring. Also, *thank* you for recognizing that something's up and listening to your doctor about something like this. My mother has suspected that I'm autistic since I was a little kid, but she didn't want to "label" me to make me feel different - spoiler alert, I knew anyways. Now as a young adult, I still don't have an official diagnosis because I don't have the time or the money. I wish you and your kiddo the best and hope you get the correct results from the evaluation ❤️

Loop earplugs are great, they have a bunch of different types for different kinds of noise canceling. They have some specifically for kids as well. Good alternative to wearing headphones all the time so she can still hear what she needs to but not be bothered by excess noise. There's also a wide variety of fidget toys to choose from. I personally love them even still as an adult, and they're a nice distraction to ease the mind a bit. I've personally struggled with tactile sensory issues since kindergarten, that could be a bit more difficult to tackle depending on the person. If it ever becomes an issue for her, things that always helped me is painted nails so I can't feel my bare nails, especially when wet, lotion at all times, wipes and hand sanitizer so I can clean my hands often, and things like slime/clay/putty of some sort to feel and play with. Materials for clothing and towels is a big one as well. Seamless socks, making sure the material of clothing feels okay to her, getting softer material towels. A lot of this comes in later but it's good to be prepared, I wish my parent had this knowledge when I was growing up. Thank you for putting in the time and effort to think of your child's needs, it really makes a difference and you're gonna do great!

Start asking her if she can point to the problems now if you havent already, some sensory issues can seem like they come out of no where and she'll likely know what it is better than you will even if she cant verbalize it in the moment. Noise cancelling headphones would help and probably so would a "quiet corner" type deal that has a variety of stim toys and a comfy place to sit and/or enough room to body stim like spin around (chewlery/teethers, spinners, squishy toys, toys for sorting/counting/lining up, soft stuffed animals, favorite books, Ect all good stim toy options) and is in an area away from sound, especially too many electronics. Extra points for a snack bin. That way she can put on her headphones and go there to self regulate safely.

Like others in the posts suggested, noise canceling devices are quite useful ❤️

As someone who has been diagnosed with high functioning Autism Spectrum Disorder since I was a little kid, as far as help for the sensory needs go I would recommend a corner or boxed in area with a ton of pillows she can have pressure support, as applying pressure can help self sooth. Weighted blankets and stress balls help too. Now as far as what is causing the sensory issue it could be 100 different things, but if you think it's something you can't hear, when I was little the buzzing from fish tanks, light bulbs used on lizard and snake tanks, water filters, TV static, and coffee pots would cause some problems for me before I grew used to them as I grew older. I still can't work anywhere with fish or lizard tanks though.

Reduce the amount of noise around the house as you can. I struggle with the buzzing of neon lights and broken charging cables. Turn down the base when listening to music with your child as that could also be hard to handle. At least from my experience with sensory hypersensitivity.

I can hear the high pitch noise from a TV being put on standby. Solution throw out the TV or turn off at the PowerPoint.