We report on the low-frequency electronic noise properties of individual multi-walled carbon nanotubes (CNTs). We present experimental evidence of the key role played by the structural quality of the tube and its gaseous environment on the excess noise level. By tuning the Fermi energy location in the electronic band structure, we also demonstrate the energy dependence of the electronic fluctuations in CNTs. Large random telegraph noise can be activated under specific Fermi energy locations. The role of mobile atomic-sized defects in a coherent transport regime is discussed.