No matter how many years you camp or backpack unusual sounds at night can make you take notice. It's very normal and simply part of our survival instinct, which is a good thing. It's important that you understand that the odds of that noise turning out to be a hostile animal are very rare. I've backpacked and camped for several decades and the most common culprit for those noises usually turns out to be deer.
If you still have a difficult time sleeping without knowing the source of those noises I would suggest getting a canister of bear spray and keeping it next to when you sleep. It's not a bad thing to also have in your pack when you go hiking. I've had many encounters with bears over the years and also cougars (one as close as 125 feet) but have never found a need to use my spray but you may find it gives you some comfort.
As noted above, stay calm and enjoy the wonderful sounds you find while camping.