Mame does that sound all the time. There's nothing wrong with your speakers.

Is it the problem where the sound sounds like it's "doubling" or slowing down like a tape being eaten? You either need a faster machine, or need to shut down some other running programs.

no I don't know how to describe it in english, but the sound is more like if my speakers were not working properly, it is like a 'frying noise'

You will need to right click the game and select "Properties". On the "Sound" tab, increase the latency to 2 or 3. That should fix the problem. If not, then you need a better pc.

Most of the versions of MAME will mess up MK game sound in the sizzling kind of way you mention. I haven't tried all the newer versions of MAME so it could be better in those, but in general its something that happens because of mame, and doesn't have anything to do with how good your computer is.

I've noticed that the sound "warps" on newer versions of MAME, whereas you get the "crackling" and sound doubling with the older versions. At least that's how it is on my PC.

Download a later version, like .82u1 or later, and there will be no sound glitches, however, you might experience significant sound delay early in the game and it syncs up eventually. Increase the volume within the factory settings to about 90%, if you got too high, the actual game's bass garbles a lot of the sounds, this even happens in the arcade, particularly during Nightwolf's Light Pillar fatality.