First issue? (AC)

Well being it is really hot outside (95-100 last few weeks), I have been using the AC a lot.

I have noticed that lately when the AC is on and set to a lower fan speed (1-3), I get a random hiss that sometimes seems like it occurs when I accelerator. It is really annoying after a while...sounds like a snake making frequent, but random loud yawns. If it turn the fan speed to around 5+, the AC blows really loud and I can't hear it.