I have an ongoing issue with my 01 supercrew 4.6l. every once in a while when i go to start it, it will make this horrible screeching noise, then i turn the key all the way off and try again and starts just fine. Last time this happened it was the starter solenoid on the firewall. replaced it and went happily along my business. after several months it came back, now i replaced it again about 2 weeks ago and has already started acting up again. I'm pretty certain it is not anything to do with the actual starter itself, ive checked the teeth on the flywheel and they are perfect all the way around. ive read several posts of owners trying to track this issue down and fix it for good but with little luck. my question is, is there an alternative to using the factory solenoid? or if there is anyone out there that has dealt with this and got it to go away permanently? any advice is greatly appreciated

 

I would suspect the starter itself.

 

Lets put it this way; the firewall solenoid is a relay that just closes heavy contacts to pass battery to the starter.
It cannot screech or create any sound similar other than a click/clunk.
Replace the starter.
Good luck.