Bluetooth has a very limited range. Make sure you are in range of the iPod. As a test, stand next to the iPod to see if the audio is okay. In some buildings, walls can intefere with the Bluetooth signal, even if the two devices are very close. In other words, if there is (for example) a stone built wall between the iPod and the Bluetooth speaker, expect poor sound quality, including break-up of the sound.
If you still have issues, makes sure that no other device is connected to, or attempting to connect to either the iPod or the Bluetooth speaker.
Certain extrenal devices may interfere with the Bluetooth signal, in particular microwave ovens, especially if the microwave is located between the iPod and the Bluetooth speaker.