That's an understatement! I use GoldWave to convert WAV to MP3, on the other hand I have downloaded quite a few MP3s from the recording site I frequent, so they'd be converted using a variety of programs and kbps settings. Apart from varying volume levels, nothing has given me anything like the pumping that you're hearing. Mind you, the biggest USB stick I have is a 4GB Lexar, maybe it *is* the size of the pen drive that's causing your problem.