Abandoned experimental facility..

As the 141 trekked through the dirt and vines of the facility, they found a cell with a plaque that wasn't covered with dirt. It was in the danger ward, but, it couldn't be that bad, could it? Soap squinted to read the gleaming metal, reading aloud for the others to hear.

"Experiment 1.. ECHO. Do not enter.." Soap read aloud, shaking his head; "Aye, tha's bullshit. "Do not enter".." He laughed to himself, looking back towards Price. But, Price was on the floor. Dead. Soap spun around quickly, kneeling down and noticing the blood dripping from Price's ears. Then, Soap's vision flickered and Price was standing next to him. Concerned, but, alive..

"You alright there, Soap?" Price huffed, extending a hand to help Soap up. Soap stood up and looked at Price, tears brimming his eyes. None of them had ever cried to each-other, but Soap was terrified.

"Price, you were just-" Soap started, hearing his voice echo down the hallway although the hallways weren't echoed in the slightest. Soap just covered his ears, his breathing picking up as he tried to think about what was happening to him. Was he going crazy?..

As Price and Soap walked next to each-other through the hallways. They heard a scream, Ghost came darting around the corner, crashing into the both of them and panting heavily. His ears were bleeding, visible through his balaclava.

"There's a goddamn thing that echoes everythin'! Everythin' they echo just gets louder, fuck! My ears are bleeding, goddamnit, my head hurt-" Ghost tried to explain before you came around the corner. Repeating everything he said in his voice as he covered his ears and screamed.

Price saw a note on the ground, terrified as he read the contents; "Experiment 1; ECHO. Do not approach. The experiment echoes everything it hears, getting louder until it can rupture ear drums and bring the victim to death. Failed experiment, do not approach. Do not approach".

"Bloody 'ell..." Price gasped, staring at you with a terrified expression.