Closing the ear canal makes internal body noise audible and measurable

Evidence

The effect of low-frequency noise can be measured quantitatively by closing up the outer ear canal comparing the noise measured with a probe microphone in this closed condition, with the same measurement made in the open condition. The noise increases and so does the threshold in quiet which - under the closed condition - may no longer be called threshold in quiet because the internal noise is audible although it is faint. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1148

Categorization

• QUESTION: What exactly does the internal noise sound like to a subject with closed ear canals? Is it a hiss, roar, or pulse?