A number of phrasal verbs refer to different ways of speaking at length. A relatively informal example is the verb to bang on, meaning to talk about something for a long time in a boring and annoying way, as in ‘Is she still banging on about the neighbours?’
The verb to rabbit on also suggests speaking for an excessive amount of time about something in a way that irritates the listener, e.g. 'What is he rabbiting on about now?’
Similar in meaning to the first two examples are the verbs to witter on and to prattle on, which also suggest that the topic being talked about is trivial or silly, as in 'Why don't you stop wittering on? I'm trying to concentrate' and ‘We still hear government ministers prattling on about building new houses on flood plains’.
If you harp on about something, the suggestion is that you keep complaining about it, as in 'He's always harping on about the need to reform the economy'. If the speaker’s voice is as boring as his or her topic, the verb to drone on can be used, as in ‘He spent half an hour droning on about what the team objectives were’. And if the speaker’s train of thought is not particularly clear while he or she speaks at considerable length about a particular topic, we can use the verb to ramble on, as in 'There he was, rambling on about ley lines again'.
The use of the particle on in each of the above examples, emphasises their continuous nature.