Do you get a lot of “snap, crackle, and pop” with your audio connections? Do you hear disgusting noises when you touch or rotate an audio plug that is connected to your mixer? If so, you probably have oxidized connectors!
Do yourself a favor and order a can of Caig Laboratories’ Deoxit D5 contact conditioner. Amazon has it in stock, it’s eligible for Prime. It’s not cheap, but it lasts a long time.