I agree. There's no difference at all.

Native speakers use these words interchangeably, and we instinctively choose the one that seems to fit best into the sentence. In a spoken sentence, it might depend on the rhythm, while in a written context, it might depend on the other words in the sentence. For example, if your sentence contains the word 'one' a few times, it might be better style to use 'somebody' - but it really doesn't matter.

Research has shown that we tend to use 'somebody' slightly more in spoken and informal contexts and 'someone' more in written and informal ones, but this isn't especially significant. In fact, you can use either one in any context. This also goes for nobody/no one, anybody/anyone and everybody/anyone.