Wharfedale Valdus 100 Bookshelf speakers broken - crackly sound +

Pair of Wharfedale Valdus 100 SE 100 W bookshelf speakers. Sound starts to distort when volume is increased - not sure why but could be fixable. Speakers are otherwise in good condition. Comes with dust covers which are not pictured. Sold as a pair. Comes from a pet and smoke free home. If you have any further questions please feel free to ask.