Congestion maybe. Acute ringing or popping sensation can occur when the estuchian tube is congested due to cold, sinusitis, etc. Leading to pressure differences between the inner and outer ear. In children, this can potentially lead into an ear infection or otitis media. Have your pediatrician check the ears.
Popping Ears. Ringing and popping ears are usually plugged ears, due to blockage of the opening from the back of the nose into the middle ear space, a plugged eustachian tube. Go see your child's pediatrician or see an ENT doctor. An ENT can also check hearing to assure there is no hearing loss.