Is hearing an internal whisper that curses God when performing certain acts considered disbelief, given that refraining from these acts stops this whisper?

These are whisperings from Satan, so do not pay attention to them and push them away from you. You do not become a disbeliever merely by them, for the Prophet, peace and blessings be upon him, said: "Indeed, Allah has forgiven for my nation whatever evil thoughts occur to them, as long as they do not act upon them or speak of them." Do whatever permissible things you wish without being bothered by these whisperings. If you do not feel at ease, know that Satan wants to exhaust you and disturb your life. So, you must strive against yourself, turn away from these whisperings, and not care about them.