Try connecting the speaker to a music source using a stereo audio cable plugged into the Line In Audio socket of the speaker and the headphone socket of a mobile phone (for example).
If there is no noise, there may be a problem with the Bluetooth connection. Remove any pairing connections stored in the speaker and also the Bluetooth device (e.g. phone) (see previous answer to you with User Guide link) then re-pair with the Bluetooth source and see if it is still noisy.
If it is still noisy, remove the Bluetooth connection 'stored in the speaker and try pairing with a different Bluetooth device, (ensure that the 1st Bluetooth device has the Bluetooth turned off) and see if the noise is still present.
If there is noise when using both the Bluetooth and the stereo cable there is a problem within the speaker. There are a lot of things in a powered speaker which, if faulty, can produce unwanted noise and it would have to be opened so that it could be checked to see what is causing the problem