The "WHOOP WHOOP" sound is only indication of disconnecting autopilot you need. Once that is there, no need to push disconnect more time (other than to silence the sound)

check the system page on the eicas,sometimes [a lot really] my yoke is pushing left or right, replugging it in, fixes it for me.Check your hydraulics page basically

Okay, I've done a lot of remapping of button presses. I don't know what the default is. If it was toggle AP, then I changed it to disco only. I engage the A/P on the yoke and disco w/ZZZ. Prolly only need 2.

Wake turbulence?John

Were you landing by a nude beach? Maybe all the pax went to one side to look out the window...Alex Bart

Well, I wonder if this is the same problem I have been having with the final half mile or so? The aircraft veers left at an ever increasing rate until I land with as much as fifteen degrees of crab - or more! However, after trying scores of times I have concluded it is something to do with the changing viewing angles on the approach whilst using Track IR. This severe drift does not seem to occur when the viewpoint is fixed and, strangely, I have not noticed this problem with any other aircraft.William Evans

hmm i think the autopilot cannot be the problem. he stated, that he cannot keep the plane level by any means. that means, he tried with full deflection. the autopilot will disconnect automatically at a certain pressure on the yoke.