The SAI is a emissions device, it forces fresh air into the catylictic convertors to help them get hot faster, cold cats dont reduce emissions, hot cats do.
There is a air filter ontop of the SAI pump, if it gets clogged it will make the pump noisy.
There is a thread around here somewhere with a how to to replace the filter.
This pump will come on when the engine is cold and run for a few minutes and then shut back off.
jyclasas (spelled it wrong but close, he couldnt choose a simple screen name lol) is the one to get ahold of to repalce the filter, he has pics and everything.