I have no experience of wireless speakers but I think you should contact the seller, if the unit is still under warranty or perhaps the support section of the manufacturer's website.
Certainly do read the instrucion manual.

I am guessing but either the wireless signal is being lost (depends on the function of the blue light) or the subwoofer is malfunctioning after a few minutes and the built-in thermal or overload protection is switching it off. The thump sound could be it trying to switch on again and finding the fault is still present.

Just my thoughts...