hey

I experience thoughts as vibrations all of the time. The vibrations originate in (what feels like) the middle/base of the brain, and as they move up they eventually transform into thought.
I don't think it's your imagination, but even if that's the case, I always found it good to remember that my imagination is part of reality, since it's happening in my brain, and that I should meditate on it like on anything else. It is impermanent, unsatisfactory, and arises by itself.
Bruno