what causes a loud flapping sound like tire is flat when car accelarate to 55-60

Could be a wheel bearings or a bad tire. Something loose in the suspension could cause your issue as well. Hands on inspection at a shop is needed. Here is a link to find a shop near you. https://repairpal.com/repair-shops Alex

Something's flapping in n the wind!

Check the engine bottom cover on the underside (between the engine and the road). Mine was blowing down onto the road and plowing until I slowed down. Sounded like a tire coming apart. Fasteners were missing on the front left corner. I believe this "pan" has to come off to change the oil filter and sometimes fasteners are lost or loosened.