When I run my AC at any fan speed under 4, there is no noise, but greater than 4 it seems to have a noise in which a leaf is stuck in the car or a baseball card is attached to a bicycle spoke. Any ideas?
Someone taped a playing card in the blades' path?
Imbalance doesn't sound like that. Slight positioning error, under more pressure blades interfere with something? S/b minor fix.
If you hear a periodic tapping, it's likely that a plastic baffle, spring clip or nearby wire harness has shifted, and it grazes the fan blades.
At higher fan speed the rotational acceleration on the blade mass stresses and alters their shape, bringing it just close enough to interfere.
I had the same issue on one of my Mercedes and it was a quick fix at the dealer.