1968 Plymouth Barracuda

Happy Fathers Day All! Posting today because yeaterday I had a problem with my alternator. After about 5 minutes of warm up the brushes on the back of the alternator would make such a high pitch whisle. Now mind you this is a referbished alternator from Napa, an identical match to the one I took off in January. Lost the recipt and took it to Napa anyways. They rang it up on the computer and decided to trade me for a new one calling it a defective order. I hope there are some of you that read my thread updates here... Will this happen again? What kind of alternator (output) are you running on your Mopar? I am using stock wiring harness with an MSD 6 ignition. Thanks for any advice!