Bearing(s) going down the tube?

Ok recently (last night) I heard a sound coming from my case that sound like a frog croaking, or even better a hard drive seeking, but low frequency, low noise. My cheap microphone can't pick it up but it's annoying. I tried different fans and found out its the fan on my VGA silencer. On high speed it makes this noise but not on low. Could the bearing(s) be going out, or is something else causing this? I don't think its dirty because I've cleaned it recently.

sounds like it's struggling/dying...

Try using some 3n1 oil to lubercate it.