Herbi overflow making noise

[Palmer]

I set up a tank 2 months ago that had an external herbi overflow and is now starting to make a lot of noise. Please see pictures below. I havent installed a new pump and I do not think there is anything clogging the return pipe going to the sump. Looking in the top the water is freely moving down to the 45 degree elbow shown in the picture. I am not sure why all the sudden it is making all this water flow noise but I was wondering if there is someing I can put on or in the pipe to help quiet it downa bit?

Palmer