I've had the same problem LWB, not much you can do. I had it happen with a Rio 400, brand new in the box. No matter what I did it was noisy. It drove me nuts. I took it back and got another one, same model, this time it was fine. Must have got a lemon first time round.
90 gallon, Crypt undulata "broad leaf" Lobelia cardinalis small and large form. H.corymbosa "compact" Crypt parva, Crypt Red Wendetti Downoi, Bacopa, Samolus Valerandi, Limnophilla Aromatica Alternanthera Reineckii lilacina(purple)
2x 150 Wt 10000k HQI Metal Halide, 2x 65 Wt 6700k-Colourmax