a "vocoder" does not give you that type of effect.
It would be helpful if you gave an example of the sound you are talking about.
It sounds like you are looking for a "tremolo" effect (a common guitar effect) which basically brings the volume level up and down synched to an LFO.
also, many filters can achieve this effect where they cut frequencies in and out based on an LFO or a midi tempo.
Also, you can cut the level in and out with a gate... you will probably need to manually automate it.
Or, you can simple make a volume curve in your sequence on the track you want to effect that cuts in and out... many sequencers allow you to draw waveforms synched to your tempo in the automation section... just draw a sin or square or whatever wave (depending on what "shape" sound you want) in the level automation section.
Or, you can cut away pieces of the audio that you want to effect.