New serpentine belt, still noisy

Just replaced the drive belt on my 2001 Toyota Echo, 100k, AC. First replacement as far as I can remember - don’t know if a shop ever did it in the past, but doubt it, and did this change myself.

I opted to replace because, 1) it seemed about time, and 2) I was getting some belt screech before the engine warmed when it was cold and damp out.

But, now I have an even worse screech. I’ve only noticed it happening at night (alternator resistance from the headlamps?), when it’s cold and there’s dew on the windows. It’s intermittent, but increases in volume under load (initial acceleration from stop, or downshift to engine brake). I thought it was connected to the dash fan being on, but apparently not, as the sound is present (again, only on cool, damp, nights) when the fan is off, both AC on and off.

One last detail - I may have a bit too much tension on the belt. In this car the tension comes from pulling the alternator away from the engine, and I had a hard time getting a good reading on my tension indicator. I’m likely at the high end of the recommended tension but may be exceeding that to some extent.

Thanks in advance for your insights!

It’s was probably a bad pulley all along. It would sound just like a squealing belt. Something that runs off that belt is probably on it’s last leg. My bet would be the air conditioner compressor.

As Whitey said its time to start looking at the pulleys. In general you will probably find this to be useful:

Have your battery checked…If it’s weak or has a bad cell, it will put a much greater load on the alternator as it tries to compensate…

I’d check the condition of the bearings in the pulleys, tensioner, and alternator.