Look around some more on these forums, you will find other threads with people reporting the same thing - don't listen to the people telling you it's a fault.
I've got a 5950X and observe similar things, with a 360 AIO cooler. After finishing building the system I was so surprised at the temperature I thought the cooler must not be making good contact, I even took it off to check and put it back.
The issue is with the design of these chips - when they are not truly idle but lightly loaded, they use a high voltage to boost 1-2 CPU cores high for maximum performance. As more cores are loaded, the voltage drops too. I did some testing with Cinebench and the single and multi-core benchmarks, and found mine actually runs hotter with a single core fully loaded than with all cores loaded.
As alec said though, 5-10% CPU use at idle is not normal - check your system carefully, find what's using CPU time at idle and fix it. In my case, I found MSI Afterburner had started monitoring and graphing all 32 cores for use, temperature etc.. and was using a few %, as was the Epic Games Launcher. Once I sorted those out and got it truly idle at idle - like 0-1% CPU use - the temp at idle is about 40-41c. I could get it lower but have the fans on the cooler at low speed when the coolant temperature is low, I like it quiet.
