Picked up a used board with Alpha Controller quad fins. When the board picks up speed, I get a fairly loud humming sound. Have to say, pretty weird. Anybody know what is going on? Thanks

Also ensure you have no loose fins / fin boxes

So after checking out the type of fins you have, I came across this. Not sure but it looks like they're a moulded fin and probably need a sanding down particularly of the trailing edge.

Thanks all for the replies. Colas, that video was awesome thanks. I sanded down the trailing edges today and will see next time I am on the water. The fins have grooves on the trailing edge. I decided to just take them down to close to smooth. Interestingly, when I sanded the rear fins the first few strokes sounded exactly like the humming sound. Just a hunch but after sanding the grooves down I wonder if they were the cause of the humming.