I have central a/c in my house; this summer the unit outside has sometimes been making a loud, grinding noise when it comes to a stop. When a repairman came out to check in June, it didn't make the noise for him to hear so all he did was check the fre-on and said everything was okay with it.

Recently, when it does make this noise, it will now continue with a loud, metallic squeal for up to 30 seconds or more. The unit inside works properly and continues to cool. What could be causing this terrible screeching sound?

First guess fan motor bearing going out