Just wanted to add something into the mix with regards to Brian's "paranoia" at the time.
In the mid sixties a big fad was the secret agent. This was brought about by the Cold War mentality & Bond films and spawned awareness of spying & "being bugged." So when Brian Wilson though he may be "bugged" it may have been an offshoot of this general paranoia that all this secret agent spy stuff helped create.
Carol Kaye talks of a party she hosted around this time where she "bugged" her own bathroom for a laugh. Reportedly, Brian was taken aback by this at the party exclaiming "No, Carol would never do something like that!" It's easy to see how incidents like this one could cause Brian to slip into paranoia.