If you have replaced the belt, tensioner and idler pulleys, then the problem could be the water pump bearing, alternator bearing, camshaft bearings, Power Steering pump or any of the items attached to the serpentine belt.
You may try to isolate the sound by listening with a length of rubber hose and place it near the areas where the 'noise' you hear may be emanating from. Just be careful not to get the hose too close to the engine fan or belts as it can get caught and cause damage or injury.
had a freind his truck did the same thing and come to find out they gave him a wrong part. i cant remember if it was suppose to be a four groove and the gave him a five belt. or it was a tensioner he had to switch the pulley off the old to the new
Most likely the new pulley is not in line with the rest.
See "Related Questions" below for more about Taurus serpentine belts - both routing diagram sources and ideas on installing them. get the belt routed correctly, leaving a loop near the tensioner pulley. using a 15mm wrench on the tensioner bolt, move tensioner toward front of car (spring-loaded) slip smooth side of the belt over tensioner, release pressure on tensioner slowly. verify belt is fully seated before starting engine.
number one make sure they sold you the right idler pulleys,,next did you align the timing marks to correct specs...if everything is the right product for that car theres nothing that should go wrong...check the notchs on the belt and count the notchs on your old pulley and the new one ... i just went through the same thing with a mercury villager ..to many notchs on the pulley they sold me ..they said someone must of put the wrong one back in the box and returned it .AT MY EXPENSE
The belt tensioner needs to be replaced along with the belt and adjusted correctly. Procedures for this can be found in a chiltons or Haynes manual for your vehicle.
fan clutch?
defective alternator
check your timing
Check the fuse
check your engine balancer pulley on the left side of the engine. It is the big main pulley on the very bottom of the serpentine belt. This pulley has a rubber dampener inside of it and when the rubber breaksdown, the pulley becomes loose and makes a banging or clunking sound as the engine is running. Don't know for sure if this is your problem but its worth checking and it is simple to do
It replaced placing ice in a cooler to keep your refrigerated items cold.
most likely warped rotors,have em turned or replaced