There is a plug on the front cover, take it off. The fluid should be about to the level of the bottom of that hole.
If I were you I would drain it, inspect the fluid and fill it back up. Should be a pretty simple operation for you since you have done that other work. There are multiple write up threads around here if you want specifics on the process.
Another possibility is your front drive shaft. What are the specifics on your jeep? (fill out your profile so we can help you easier)
If your driveshaft looks like this:
That may be the issue. The rubber boots at the ends crack and the grease leaks out.
The driveshaft and a bearing in my front diff were causing a noise similar to what you are hearing.