sound insulation for impact noise on aluminium door sill

[fionae]

I've just installed an orangery which has powder coated aluminium doors. The sill below the doors is hollow and whenever it rains the water dripping from the fascia above the doors on to the sill impacts like a drum. It is incredibly noisy. Unfortunately I can't call the company who installed this in to sort it out as they have just gone into liquidation!.

Any ideas on how to reduce the impact sound would be gratefully received. I wondered about stuffing the hollow sill with fibreglass - this will not be easy because there is not a lot of room either side of the sill ( which is 3500mm long). I'm reluctant to do that until I've had someone else's opinion as to whether this will work.

Running a gutter across the front of the orangery is not an option as it will look terrible.

I've searched all the Diy sites and can't find any advice, but with all the orangeries around these days someone else must have had the same problem

Many thanks