I'm using sox and toolame to convert the audio from 32Khz to 44.1Khz and I get a pop at the beginning of the file when i do this. Anyone know how to prevent this?

This is the command I'm using (within a batch file)

mpg321 $filename -w - | sox -c 2 -s -r 32000 -w -t wav - -r 44100 -t wav - | toolame -e -p 2 -b 224 - output.m2a

any help would be appreciated, thanks!