RS41 weather balloon unable to decode data

Some times ago I tried to decode the signal from a weather radiosonde (RS41) passing in my area using a cheap RTL SDR (using both standard antenna and a home-made one, with similar result).

The recorded audio file is this one, it's a bit noisy, but the transmission is clearly audible. Using the RS software I wasn't able to decode any data, whereas it works perfectly with the example wav file that is in the same repository (after suggestions from here).

The command I used was like sox wav/20140717_402MHz.wav -t wav - lowpass 2800 2>/dev/null | ./rs41ptu -i --crc -vx.

I also tried reducing the noise using Audacity, but without any success.

Is it a software or hardware/noise problem?

Thanks and sorry if it is a trivial problem, but I'm a beginner and I wasn't able to solve that in any way.