The other day while trying to kill time and stay a wake with the stereo at a moderate volume the sound started to fade in and out with the complexity of the music and then reduced volume and became very distorted. I reduced the volume for a bit and returned and the speakers sounded fine for a minute then repeat. I have been looking for a reason to replace the speakers but I would like to be sure that this is the cause
Speakers are stock head unit is a kenwood mp922

That sure doesn't sound like a speaker problem... sounds like your head unit (or amp, if you have one) is dying.... or maybe overheating and protecting itself.