I could really use some advice or if this has happened To anyone els...

So during my pregnancy my sister came to visit with my 2 year old nephew. My soon to be 3 year old soon was fine with all the crying, screaming and talking his cousin was doing. Then one day any sound my nephew did my son would throw a fit, crying and throwing him self. Got to the point I needed to put him down for a nap. Well they ended up going home and a month later I have my baby. Anytime the baby makes any noise my oldest FLIPS out I mean tantrums, throwing him self and very loud screaming. My husband is home for a few weeks thank goodness because I definitely couldn’t handle him with the baby on my own. We tried taking him out of the room And talking to him l( how he can’t act like that, it’s his brother he i a baby and baby’s cry a lot) but if he can hear the baby still is crying, tried distracting him, tried ignoring him, giving him more attention, right now we are on trying time outs every time he is screaming. He has no problem with his brother he’ll come over and touch him it’s only when he makes sound. Last night he even got upset the dog keep sneezing. Thought maybe he missed me since iv been busy breastfeeding so was playing with him a lot yesterday and still same thing. Btw baby was born on Thursday so hasn’t been a few week yet. With my oldest he is used to it just being the 3 of us because we don’t have family who visits and me and my husband would To were we don’t need babysitters so it’s a big change. Just don’t know what to do anymore. It’s been very upsetting. Can anyone help?