Sometimes when lie down from left side i hear in my ear a very fast beating like fluttering.faster than heartbeat.when i turn side or open my mouth it stops.it is not very annoying but i dont know what it is.my ent says it is middle ear spasm?

Usually benign: You most likely have what is called "pulsatile tinnitus." In a person your age, with no heart of vascular problems, it should be a benign condition. You did the right thing to have an ENT specialist evaluate it. So, this should be considered a aggravating condition. In almost all cases, although there is no treatment, it tends to come and go.