Noise Like Rain

by Charles M
(Troy, Alabama)

There is a noise near some ceiling vents that sounds like rain on a tin roof or perhaps like paper being crinkled in your hand. It is quite noisy at one vent. Less so at another and seems not to be at all in the others.

I have changed the filter recently (we just took possession of the place), but it is still making the noise.

There is no liquid leaking. It is not the a/c unit - it's near the ceiling (a dropped ceiling with acoustics tile).