This claim returns every few months and always makes me laugh a little. I studied Acoustic Engineering for 5 years on AGH University of Science and Technology, PL, and the uni had its own anechoic chamber. I'm pretty sure it's not as isolated as the one holding Guinness record, but it really is completely quiet nonetheless.
The amount of time one had to spend there sometimes easily exceeded one hour; several PhD students did stone studies on for how long can they stay locked there in complete silence and darkness, one person at time - they made it through the night and didn't lose their sanity.
On another note I always find it a bit strange that many people can't hear/feel their own pulse with little focus and require a chamber to experience it.