When I exercise and strain (like when lifting weights) one of my ears gets hollow sounding. It often gets so bad that I cannot even talk to others at the gym because it sounds like I am yelling when I talk. This condition only occurs after exercising for about 15 minutes, it does not happen when I run or swim, only when straining is involved. It tends to go away after about 10 minutes of rest. Why does this happen, what can be done to prevent it, and am I doing damage to my ear when this event occurs? Thanks,