could just be tinnitus. is it high pitched ringing and you sometimes go a little def as a result? i get it sometimes, and i have many friends and family who do, it could be genetic, ear infection, wax buildup, but normally today the cause is loud music, either from concerts, or wearing ear buds.
if you think it's an animal crying, like it only happens at night, you could try leaving an offering, or doing a cleansing in your room. if you think it's a cat, a saucer of cream or something. try meditating and see if you can sense anything.
Could also be a calling of some sort. People who have empathy and sometimes feel things like that that seem real. It is possible to pick up on an animals emotions. Do you have animals in your house or near by? Can you identfy the animal?
If the sound is frequent throughout the day or constant, first rule out a physical problem and go to a doctor. Can't hurt right? If it does happen consistently it does sound like common "ringing of the ear" which could be a sign of a serious health concern. We all get it once in a while for a short interval of a minute of so when blood rushes through our eardrum or in superstition, someone is talking about you!
I always like to mention the physical explainations first.
I know all too well about noise and sleeping. Its when clairaudience is loudest. Just the other day I was in the middle of a nice dream and heard a loud clap directly in my ear! Sounded like when you slap books together. I jumped up and asked my husband (who was in the same room awake) if such a noise had been heard by him and he said no. It happens randomly...giggling, talking, laughter, whispers, shouts, screams, random noises, you name it!
If you're clairaudient, the best advice I have for you is to do a full house banishment and then ward/protect your room and the whole building. This won't completely stop spirits, but it will cause such occurrences to become infrequent by creating a barrier most won't be able to cross to be in earshot. If it doesn't stop, then you definitely have a medical problem.
I've discovered through my own experience/observations that such protections will eventually break down to specific spirits when you have photos or belongings of a deceased person (them) inside. So if you ward and after a week of peace, you start havin problems, consider all second hand, antique, or family items in your room/home. It can become a very unfun treasure hunt. Have too much or don't want to give it up? Put it all in one room and create the protection excluding that room. Put an extra ward on the doorframe for good measure. Some items can be cleared of the link, but photos and very personal possessions like jewelry cannot.