I had my component tweeter connected in reverse for about a week, and am wondering if this could have damaged them. I wouldn't think so, but I've been having issues with them and am trying to determine why. They emit a hissing sound even when the head unit is off and have done this since I first installed them.

 

No. Reverse polarity will not kill your tweeters. If the car is running, but the HU is off, and you have noise, then your cables are picking up the noise somewhere. If you have a separate amplifier, it is possible that it is noisy in itself, or that its input wires are picking up noise.



If the car is *not* running and you still have noise, and just the amplifier is on, then the amplifier is noisy.