A lot of these screchers can be traced to some heat issue. The m9300t is very similar to my HP d5000t and is about 8 years old. At that age you would get the usual million mile work done.

That is, open it up, put on a dust mask and use the canned air to get the majority of the dust out. If it is like most it's full of dust. That may be enough. If not, time to pull the heatsinks and replace all the old dried cracked heatsink compound.

Finally if the sound card has died, consider some under 10 buck USB or sound card as a fix.