My 2003 Toyota Highlander makes a high pitched screeching noise when I start the ignition (though it doesn’t happen every time and has made this noise for over a year now - yes, I procrastinate!) Someone mentioned that it might be the timing belt but I’ve also heard that it could be the alternator drive belt slipping. Would anyone know?
The teeth on the starter aren’t properly engaging with the teeth on the flywheel.
It might have been as simple as the starter needing tightening or adjustment.
Or, it might be that you needed to replace the starter.
Now that it has been a year, you almost certainly need to replace the starter and the flywheel. That screeching sound is the sound of the teeth on the flywheel being damaged.
(This assumes that the sound occurs only while you hold the key in the start position.)
No, the sound occurs when I turn the ignition and the engine starts. The noise lasts anywhere from 5-15 seconds.
It’s probably a problem with the autotensioner. You’ll need a new one of them and a new belt (that’s what making the noise). Or, you could wait till failure. If you do, you won’t be driving to the shop of your choice, you’ll be having it towed.
You should check your manual, I doubt it is the timing belt but it may be time to replace it. The most probable cause is the serpentine belt, a tensioner, farther down the line a component along the belt path, ac, power steering etc. If you know your parts using a piece of heater hose listening for the source is one way to find the offending part.
Looks Like I type slower than you mr 60 wpm tardis 
Thanks tardis and waterboy. I knew it was some belt that was making that noise but wanted to be able to sound like I knew what I was talking about before I took it to a mechanic - guess I’ll just have to find a reputable one.
Don’t forget to check the timing belt replacement schedule in your manual!
Yes, the timing belt won’t make any noise at all until the instant of failure.