Thanks for the replies guys!
Bladerunner: Squeezing the pump inlet and outlet result in the same thing -> increased noise. As if it was already cavitating.
redleader: Yeah I'd say their is no bearing to wear out too but I think I chose the wrong word, english not being my native language. In any case you can wear out the impeller as that is what aquarium hobbyists who own magdrives have to replace once in a while, and a tell-tale sign that it needs replacing is that it is getting noisier. That's what I've heard and read ..
What I'm gonna do next is remove the pump from the system and run it in the kitchen sink with nothing attached, I gotta get to the bottom of this issue. I'll get back to this forum in a day or two!
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Pump:Eheim 1048,
Radiator:LPD radiator 100x150x20mm,
CPU block:DD Maze-2,
GPU block: DD GPU block,
Chipset block:Zalman NB32
AMD XP 1500+, EpoX 8K7A, PoV GF3Ti200
Pic of my YY-cube