1996 buick regal fan belt slipped off

it depends what kind of noise, if its a licking noise the pulleys that the belt is being turned by could be bad (belt tensioner pulley ,Idler pulley etc.) if its a squealing sound like a high pitched whistle or like a rubber heal screeching on a tile floor constantly the belt is no good there is fabric on the inside of the belt and when it wears away you will get the chirp or squealing /screeching sound from this. inspection of that belt will tell you look at the grooves if looks like shiny rubber you found it if it doesn't and the fabric is there then a pulley is the problem bad bearing can make the belt slip resulting in the squealing good luck LATER MAN!

Possible water pump. Remove the belt and grab the pulley , wiggle and spin. Check the other pulleys as well.

The idler belt can be loosed out on the main pulley circuit which allows the belt to be pushed into the slot and then the idler can be pulled up to be tightened to the desired tension.

Look closely as there should be a square one half inch or three eighths inch hole in the tensioner. Place the proper sized ratchet or breaker bar in the hole and turn which ever way loosens the belt. When replacing the belt be sure the belt is properly settled in all the pulleys as if it's off by one spline on any pulley it will quickly damage the belt. Please rate this answer, thanks.

There should be a feature that looks like a bolt head on the pivot of the spring-loaded idler, which will allow you to move it so that you can put the belt on.

Optionally, you can get a bar on it, push it against the spring so that you can put the belt on till it runs into the bar you're using — far enough to stay on when the bar is removed. Then push on the side of the belt to move it fully onto the idler. (A person to help you can be a real benefit.)

Hi, best to get a shop manual for this operation, if you have not replaced it before. Usually there is an "Idler Pulley" on many late model cars that is "spring loaded".
You "Bias" this pulley (usually with a socket wrench) so that the serpentine belt has enough slack in it so you can remove it. Then you disconnect the Positive Battery Cable, disconnect the "Field Wire" harness and positive battery lead from the alternator, unbolt and remove the alternator.
Reverse procedure to install new alternator.

Take care

your problem is a result of weak/poor idler tensioner operation due to a weak spring in the idler tenisioner and need to be replaced

buy a new tensioner assembley and idler pully and might as well get a new belt while your at it. you will need a 3/8 ratchet a 15 mm socket and a 13 mm socket there is one bolt holding on tensioner remove it discard old tensioner put new tensioner in place and tight bolt. second remove bolt from idler pulley discard old pulley put inton place and tighen bolt. next install belt fallow belt routing digram put head of 3/8 rattachet into hole on tensioner or on bolt head of tensioner pulley depending on style of tensioner and pull or push to create slack in belt push belt into groves on all pulleys and release tensioner

there is an 8mm bolt right under the alternator. loosen that up then loosen the bolt on the idler pulley and itll come right off

The first thing i would do is try playing with the belt tensioner. it sounds like the belt is lose and when the engine warms up the belt starts to expand and slips off.