What is the tank sitting on? I found a filter became noisy when I shifted a tank onto a less dense cabinet. Perhaps it is vibrating with resonance (or whatever) with the stand. What sort of lid is on it? Are you able to put a small piece of wood, metal etc across the top corner of the tank then hang the filter from this with a bit of string or fishing line? Arrange it so it is almost, but not quite, touching the glass.