Grado GR10 (at roughly 20 hours of loud burn-in)
No. The lowest frequency I could detect was about 30 Hz. Interestingly, I could hear a change in the amount of static when I started the tone. When I increased the frequency past 30 or so, they kinda "crackled" as if saying "oh yeah, what? I was asleep. Do you want something?".
There's something wrong with either your seal or your GR10 imo. Like all moving armatures, the Grados roll off below 30Hz, but produce still a little amount of rumble at 20Hz. I can easily detect it on my GR10 at medium volume.