elmwood - I wrote this for the sailors that are going into the CT rating, but it will probably help you too...
No one ever came to our house, my son is a FC and he has a secret Security Clearance
elmwood - The ratings that do come to your house are:
CTI, CTM, CTN, CTR, CTT, IS, IT, SECF, MT, YN.
These are the rating that have Top Secret clearances, along with SSBI access. The SSBI is when they come to visit. If you just need a Top Secret, then they won't be visiting since it's all just a records check. The investigators work for either the Office of Personnel Management (OPM) or the Defense Security Service (DSS), and the actual investigators are usually contractors, not actual government employees. None work for the FBI.
Before my sailor left for bootcamp he was working full time and a friend of his was in bootcamp. An "agent" came to my son's place of work and questioned him. They had been roommates and fraternity brothers, both left college and both joined the Navy.
Freaked my son out a little when they showed up at his work, but all went well, general questions mainly.