Last year (sometime in December) my car started making a humming sound when it was low on power steering fluid. The problem went away when I refilled it, since then the issue has occurred twice more (once in the spring and just recently again). Every time I check the level, it's under the "Min" mark and every time I add more in I add it up to the "Max". Since until last year I never had to do this, I decided to check the Audi maintenance schedule and it says that power steering check/refill isn't usually due until 75k miles. Since my car only has 55k miles on it, I was wondering if this is normal or if you guys think there is a leak? If it IS a leak, it doesn't seem to be leaking much since I'm still using the same bottle of fluid I bought last year.