Tubes sound like a broken lightbulb

So I just bought some pretty fancy NOS tubes from a big online store. I unpacked them and notice they sound like a broken lightbulb 💡 when I handle them. Is this normal? I paid a lot for these tubes Because they were promised to be and test as brand new.

the tubes are Slyvania Jan-chs 6sN7gt / VT-231 2 rivet “bad boy” tubes

thanks for the feedback