Firstly check that your skimmer isn't touching the glass sides of the sump, specifically the motor. You can also raise it slightly with a this piece of foam. If you have done that you could try cleaning the motor/pump. If that all fails then it's time to replace I guess. I found my skimmer to be loud as heck if it was touching anything, isolated from the glass it's silent and works great. It's an swc skimmer and I like it.