your wording in this is slightly hard to decipher... but if the timing belt had slipped the engine would back fire and run like crap or die depending on how bad timing jumped. timing bbelt has very big grooves that wrap around gears they grip pretty aggressively. I doubt its your timing belt unless you have issues...... the loud squeaking noise sounds like the drive belt that runs the alternator and powersteering and a/c stuff is loose... the belt is loose... make sure you installed it correctly and tight when you installed the new alternator. try moving the belt by hand see how loose it is, you may need a new belt tensioner.

sometimes if the bearings going bad on some thing it will squeak but I think its your belt loose or not put on correctly. when you changed the alternator you had to of removed the belt and it may have came off some where that you didn't see... just recheck the belt that wraps around alternator.

Your timing belt does not have enough tension have a mechanic change it also change your oil and transmission fluid

Check belt tension-er and belt. OR take car to a reputable shop. Obviously, your wasting time and money and getting no where.

reputable shop

Hey I have a 2001 impala and recently it wouldn't start. Turns out it was my alternator draining my battery to the point it wouldn't make a sound when the key was turned. So I've installed a new crank relay, starter, battery, & alternator.

After all that I got it started. It stalled a little but it turned over. After this it started makes this loud squeaking like noise when the gas is pushed. Then it turned off. I figured it was my timing belt.I tried a few days later and it sounded as if I was revving it up.

Any ideas on what this noise could be?