cracked celling

[Mary Ann]

Purchased home in 2003, within 5 months there was a crack where the two units joined together, this is only in the front -about 15-16 ft. There are also seperations between the wall and celling. Had it patched, handyman used calulking -did not work- Had a co. come in to check leveling & tie downs are tight - - unit is level. there is also a cracking sound coming from the air ducts, when air/heat is not on. Before I have the drywall repair what could be causing this problem