When I play my high E string from the 18th fret and up the note doesn't even sound it just screeches instead. I just changed my strings today and I was having the same problem even before I changed the strings. I am using Ernie Ball Hybrid Slinkys on a 2008 Squier stratocaster into my Peavey Classic 30. This has only been happening the past week. Does anyone have an idea of what's causing this problem and how I can fix it?
Going to need a bit more detail. Are you playing with distortion? Is the guitar set up properly? And by properly I mean you used the actual specs from the manual or Fender's website (assuming you set it up).

If so, the only thing I can think of is maybe a high fret if its set up properly.
I'm always screwing with my rig. Muh chilluns:
Warmoth NRFR strat JB/Jazz
Mesa Boogie Royal Atlantic, Diezel 2x12
Turbo tuner, J Cantrell wah, Alesis 3630
Green Rhino, Wampler Velvet, Strymon ElCap/Lex, Phase 45
Screeching noise?

1. Your wife, telling you to turn that damned thing down.
2. Flock of parrots that's in a mating mood after listening to you try to play guitar
3. Zombie infestation. Starving. No brains around.
4. Car chase filming outside your window.
5. Baby needs a diaper change and a bottle.

You probably have a setup issue related to frets that aren't level, a nut that's cut too high, a truss rod adjustment that went horribly wrong.