If it's not Bees or Bacon frying (buzzing/sizzling) then it's an electrical problem, check your connections at the battery and the regulator maybe the starter motor that's my best guess anyway, any earth wires that might be loose can do this as well, your in for an interesting time looking for this type of fault cos you have to get your ear down to where the noise is (or you think it is) and turn it on and guess where the noise is coming from then tighten up anything that's near and try again till you find the connector that's playing up. Might be an easy fix, good luck.