I am attempting to upsample data sampled at 24kHz to 44Khz. I intend to upsample by 11 and downsample by 7. When I try to do this, I can get what I want but the output sounds extremely noisy. There seems to be a background hissing sound. The anti-aliasing filter has to be designed at 264kHz as a result of the upsampling. Can this be causing a problem. What is the best approach to this problem?