Hey guys. I finally got around to modding the fans in my cv5000. Bought some Noctua fans and wired them in series for 24v on the amp. They seem great but I hear this scratching sound. It's intermittent. Definitely nothing rubbing or touching the fans. The sound is audible when power is applied to the amp. As soon as I turn off the amp the scratching sound disappears even though the fans are still moving. I can't figure it out. I'd like to fix. The fans are nearly silent but the scratching is audible enough to be annoying. I've uploaded a video. Please help. Thanks.