What Causes Echo Effect In Ears?

Hello dr,
when i cover my left ear with a pillow or anything and hear a noise from the right ear at the same time, my lefts ear repeats the sound.
I have this condition for a very long time and it started after i suffered with cold that made me stay in bed for almost 3 weeks.
Can u please tell me what is going on with my left ear? why is this happening? and is there a cure?