Why do I hear beeping sound at my ears, with sometimes at the left or right one?

Not unusual. It's not unusual to hear a high pitched ring for several seconds at a time. Consider it your ear retuning itself. If it is present for days or longer, it is likely that you have some hearing loss. If you have tinnitus that does not stop, i would recommend a hearing test and an exam by an ent, especially if it is in just one ear or pulsates like your heart beat.