It could be one of many things.
- If your name is similar to a person with a lot of legal problems, they may have to sort through a list to make sure none of them actually apply to you.
- If you have any violent non-felony convictions/guilty pleas, any domestic violence orders against you, or other similar items, they could be the problem.
- Heck, it could be as simple as the FBI computer being "down" for maintenance or overloaded with requests. When in doubt, a delay is probably the default option.