I had a 6900XT reference card. It had some whine with the reference cooler. When I installed the EK waterblock, it had unbelievably loud coil whine. It was so bad I literally ran looping benchmarks and closed the door to my room and I could still hear it on the other side of the door.
I sold it on this very forum due to the coil whine. When I reinstalled the reference cooler, it was basically non-existent.
I bought a Strix 6900XT hoping the different VRM components would have a lesser chance of whine. I also skipped the Acrylic waterblock and went for Acetal, as it is softer and should absorb more sound. I figured the acrylic waterblock basically amplified the sound on my first 6900xt.
Now between the Strix having some coil whine at what seems to be half the frequency (of the original ref 6900xt) and the Acetal waterblock, it's completely tolerable and quiet enough I don't really get bothered by it unless I have the case side panels removed