The bottom of the ocean isn’t as quiet as it seems. Researchers were surprised when they heard noise on dropping a microphone into the Mariana Trench 6 miles down in the Pacific Ocean.

The National Oceanic and Atmospheric Administration and Oregon State University scientists, who were behind the experiment, didn’t expect strange sounds recorded by their equipment. According to a release by Oregon State University, the scientists didn’t hear silence, but sounds of earthquakes, ships, the far away moans of baleen whales and the overwhelming screams of a category 4 typhoon that had crossed overhead.

Through these noises, scientists have got some fresh idea about what life is like roughly 7 miles under the ocean's surface. The researcher serving the US Coast Guard, sent a titanium-encased microphone over 36,000 feet down, in the deepest part of the Mariana Trench called the Challenger Deep.

On retrieving the device, the research found that the microphone package's flash drive contained recordings captured during the time period of last three weeks last summer. They got surprised again when they realized that the recordings weren't just of faint echoes, and were instead apparently discernible sounds.

Chief Scientist Robert Dziak of NOAA said, “You would think that the deepest part of the ocean would be one of the quietest places on Earth. Yet there really is almost constant noise from both natural and man-made sources”.

Dziak explained the occurrence of propeller whine in the recordings, and said that the Challenger Deep is near to Guam’s commercial shipping hub.

NOAA has conducted the mission to take steps forward in establishing a baseline for ambient noise in the ocean’s deepest areas. Oregon Public Broadcasting noted that huge research is going on along the West Coast for studying the likely impacts of increasing human-caused underwater noise on whales and other marine creatures.