First make sure the speakers are enabled by right clicking the volume icon in the bottom right of the screen and making sure "speakers" are selected as default playback device. If that doesn't change anything make sure the sound driver is up to date by going to device manager, clicking on the sound device and then clicking update driver. If none of this works it is most likely a hardware issue. Open up the laptop and make sure the plug is securely plugged in and the wires are not damaged. In rare cases the speakers themselves could be broken and will need to be replaced.
The computer could be overheating. If there is too much dust in the fan area the fan won't be as effective and will spin faster than it should be. Additionally the thermal grease between the CPU and the heatsink could be too old and need to be replaced. Try first cleaning the fan area with compressed air and if that doesn't work try replacing the thermal grease.