A survey is given of calculations on diffusion noise in double injection SCL diodes. A general asymptotic method applicable to ωτ ≫ 1 is presented that gives thermal noise at all points in the device. The method of Zijlstra and Gisolf is shown to be non-applicable to the semiconductor regime. For the insulator regime it does not seem to give thermal noise at all points in the device. The method of variation of parameters, when applied to the semiconductor regime, leads to a solution with an unknown integration constant; when this integration constant is chosen zero, one obtains thermal noise plus a g-r like diffusion noise term. Finally an approach is made for the semiconductor regime that does not neglect diffusion. The device then gives thermal noise at all frequencies and at all points in the device, plus a g-r like noise term that is negligible for long devices but noticeable for small ones.