First, make sure that the shutoff at the wall is fully opened. Then, check you're water pressure. If it exceeds 80psi, you need a pressure reduction valve, and that may resolve it.
Thanks - I tried adjusting the shutoff - fully open, 3/4 open, etc. and it didn't make any difference in the noise. The pressure was below 80 psi when it was tested at the beginning of the renovation (everything from the main cutoff on back was replaced). Are there any adjustments on the fill valve itself, or is it totally "preset"?