Every noise my daughter makes wakes up my baby

When my 7 year old isn’t home around, I have absolutely no issue putting my 3 month old to bed. Yet the second she makes a single noise, I have a wide awake crying baby. My husband and I have can full conversations, watch Movies/shows at normal volume right next to her. She just sleeps right through it without issue. I can even vacuum right next to her crib and she won’t budge!

I’ve tried to get her use to my oldest by keeping her around while I put her to sleep but I just end up with a very cranky sleep deprived baby in the end. I just don’t get it because she’s not a loud child but It’s to the point she can’t even whisper without waking her.

I don’t know what to do at this point. I’m crazy overstimulated as it is, but now it’s to the point I have to keep my oldest completely away from my baby during nap time. I even find myself always spending time with her just to make sure she doesn’t go near my room and accidentally wake her sister up. which makes me feel like a terrible mom because I should be spending time with my daughter because I want to, not out of fear.

I could really use some advice on how to get baby to be fine with her older sister’s noise the way she is with literally every other noise in the house!!!