Why do you need calibration for noise source?
I'd guess a cheap chinese noise level is dependent on temperature, input voltage..., so it wouldn't make much sense to calibrate it, if it drifts off anyway.
I mostly used my cheap china noise to display filter response on spectrum analyzer, before I got my HP 8444A tracking generator. No need for calibration there as well, just use trace subtraction function on spectrum analyzer.
A noise source is also great to track signals when repairing amplifiers.
Apart from that, I usually use clean signals from synthesizer or so, instead of white noise.