I cannot accurately answer that question but it was for at least some months. The reason is because it was so infrequent when I would get the noise. It definitely could have been low for a while, but the symptoms weren't always eveident.
IIAp3x wroteHow long did you drive it while it was making noise? if it was very very low you could have jeopardized the pump... Not to freak you out, but when the fluid becomes very low it can introduce air into the hydro lines and pump which is not good... The only thing I am not certain on is whether or not the power steering system will push the air to the top reservoir once it is filled again... It may need to be bled out like a brake line... Flushing it out is good to do occasionally anyways..
Anyone else want to take a stab at the noise?