I drive a 1983 el camino with a 1999 Chevy vortek 350 motor. Recently, we replaced the alternator and all was well. However, there has been a terrible squeek lately and I dont know what the problem is. When I put the car in gear, it gets much much quieter, but gets louder once I give it throttle. I noticed that if i turn my heater and other electronic stuff off, it slows. And eventually the squeek does stop. And sometimes it never even starts. Im at a total loss and reallyyyyyyy need some advice.
You may be due for a belt tensioner.
Besides the belt, idler and tensioner make sure pulley bearing are ok like the alternator, etc.
I’ve had good luck with the Goodyear Poly-V serpentine belts on my vehicles. They’re the quiestest of all the belts I’ve used (Dayco, Gates, etc).