I will take a shot at this but I am not a tech.
I can't download or hear your clip because I don't use Apple. If you want to try Youtube or Soundcloud or Box etc I will listen.
Without that though, the first thing you can DO without touching anything INSIDE is turn on your amp, unplug your guitar, and tap on the preamp tubes one by one with the eraser end of a pencil. Not enough to crack glass, just enough to see if you can hear the tapping sound coming out of your speakers. This could indicate a bad preamp tube but is not full proof.
After that, I would start replacing preamp tubes with a KNOWN GOOD ONE starting with V1. Then V2, V3 etc.. If not sure how to do this, simply let us know. I actually did a video of all of this if I can find it. Regardless these are 2 fairly simple steps to start with.
Next of course would be to double check all cables in the signal path, including the fx loop if you have one. Test guitar in another amp. Test amp with a different cabinet if possible, etc. Sometimes a bad power tube can cause issues too but lets start with this stuff.
Good luck,
