Check sound properties, right click the speaker icon in the notification area, playback devices, click on the speakers and select the properties tab. Under the enhancement tab make sure all sound effects are disabled. Next, under the advanced tab, try a different 'bit' quality and test, see if that makes any difference. I'm assuming you've tested the speakers on an other system. I'm also assuming you have the latest audio driver.
Surface Pro (2017) vs Surface Pro 4