I posted a bit earlier than I wanted to. I’ve amended my post to include more details.
Whether or not the person who uploaded it had permission does not have much bearing on whether or not you have permission.
For example, you are allowed to get specific permission for you to use a sound, upload it to Roblox, and mark the “make free” button. Others are not allowed to use the sound in this case, despite it being “free” for them. Only you got permission since you made a private agreement for license to use the sound.
Whether or not you can use the sound depends on the public copyright license applied to the sound and any private license agreements you make with the copyright holder. You should research any sounds you want to use to find where they originate so that you can check their public copyright license. If the public copyright license prohibits you from using the sound then you can contact the copyright holder and attempt to make an agreement for a private copyright license between just you and them.