How To Treat Clogged Ears?

When my husband plays golf or does anything outside that makes him hot he feels like his ears get full and his voice sounds like he is in a tunnel or under water. Both he and I can hear the change in his voice.

It only occurs when he gets hot. He also has difficulty doing things where he has to look up or especially laying on his back under the sink working. Our doctor has not been able to figure it out.