Sounds like a classic impeller sound. Your pump are going bad man, need to RMA that thing if it is still under warranty or buy a new AIO. This sound is typical of a AIO running too dry which is usually caused either by evaporation over time so there is not enough water left in the system (quite common on early generation products with poor tube quality but also probably on this one since it has that same type of tubing) or the system have clogged up inside so that there is no longer enough flow of water to saturate the pump head.
EDIT: Also make sure it is connected to the CPU_1 fan header and not the CHA_1 fan header. It can also make these sounds if it is not fed the proper power.