How do I deaden the sound of water dripping on metal?
If the drip is that noisy, it's probably hitting a flat horizontal spot on your unit. If you can add something to the top of your unit that is at a steep angle that the drip lands on, the drip shouldn't be as noticable.

You might be able to put a flower pot with just sand in it, or even an actual plant with soil on it on top of your unit?