[Chilow]

So...my windshield wipers make the annoying squeaking sound in light-moderate rain. The strange thing is they’re quiet when there isn’t any rain on the windshield. For example, I was driving in the rain this morning with the wipers on. It was making noise pretty much the entire time. I got stuck in traffic inside a tunnel so my windshield wasn’t getting rained on. The wipers are still on, but it’s not brushing away any rain water. There’s no noise when it’s dry.

[00Sebby]

Since it changes with the amount of moisture, it's likely the wipers' rubber. The squeak is a high-pitched vibration as the rubber bounces/chatters across the window. It's still in contact enough to do a good job and you can't see it but that's likely what's happening. You could try treating them with a blade conditioner or just replace them and see if it goes away. My '10 TE did this in light rain and I kept throwing the washer fluid to it periodically to stop it for a while.

[MAXISTYLES]

Originally Posted by Chilow

So...my windshield wipers make the annoying squeaking sound in light-moderate rain. The strange thing is they’re quiet when there isn’t any rain on the windshield. For example, I was driving in the rain this morning with the wipers on. It was making noise pretty much the entire time. I got stuck in traffic inside a tunnel so my windshield wasn’t getting rained on. The wipers are still on, but it’s not brushing away any rain water. There’s no noise when it’s dry.

Take some Steele Wool and run it few times along the rubber blade. This will take some of the surface material off and your blades will be like new.