I have a Genie GCG 350 opener, it used to work fine, now when you push the button, it "jack hammers" the door, like its not strong enough to open. With a little help the door will open. Same thing happens when you try to close, Jack Hammers again. With a little help it closes fine. Any ideas. Checked the drive gear, & worm gear and there like new. Greased the chain & track also.