Hey dont buy new speakers . Its not there fault
mines the same I think its something to do with
having to two volume controls (desktop controls)
ive sought of got round it by ... ill try and explain. If you want to listen in low volume without fluctuation turn your Audio properties volume controls down below halfway (Right click speaker icon on desktop and select) .And if you want it loud do the opposite and turn them all up!
Remember the volume device is a pretty flimsy bit of kit really I tend to leave it set at halfway and use desktop control