What is causing low water pressure in house and pump to constantly buzz in a deep well?

I do not know your situation but a good guess is that your well pump is always on and is not getting enough pressure to shut off the pressure switch. So I would shut off the power to your well pump and see if the buzzing stops and if it does then I would replace your well pump. If the buzzing don't stop with pump shut off then it could still be your well pump check valve slowly leaking threw but I think its your pump because its not pumping enough to shut off with or with out a bad check valve.