Thanks mfor. I need to do some more work on this. My config is always all good. Flaps 5 (and in FMC) trim well in the green, speedbrake fully retracted, parking brake off.
1) I heard the trim wheel noise but did not realise what was happening. When the A/C starts to move, the trim wheels spin madly and set trim to zero. This would appear to explain the horn and the difficulty in getting the A/C up to a height where I can activate LNAV, VNAV and AP1, at which time trim resets in the green and the horn silences. Cannot see what causes this at this time.
2) When I take off with standard config and nothing put into the FMC there is no problem. I can takeoff, activate TOGA and with AP1 on can fly manually or using the MCP.. No horn and no trim issues. Can't believe I am missing something in programming the FMC since I follow the same checklist/procedures that I have used since Day 1! My "test" flight uses the same flight plan, a physical config that matches your list above, and identical FMC planning every time!
As it is I am happily flying the IXEG 733 in XP11.02 (stable) and when I have time I'll look at 1105r1 again.