Care.
When anything largish such as a GS goes ooop an over the resultant weight (as you can imagine) will have one hell of impact on areas that were not designed to take such a force.
As you say that you have rebuilt the bike but that there is a strange noise that you are having difficutly in locating, and not knowing your mechanical abilities (not in the least trying to put you down) my immediate thoughts are for you to get a BMW dealer/mechanic to take a look.
You should'nt ride the bike until the fault/cause has been found.
Here are some suggestions that may or may not be helpful; remember diagnosing at a distance is difficult at the best of times.
You haven't said what model bike by the way.
1 Check the front suspension damper can operate freely, and that the damper rod is not damaged.
2 As you suggest it could be possible that 'something' has happened to the top steering head bearings, most probably the outer race could be cracked due to impact in the crash or after in the landing.
3 The top yoke could be cracked - hence the noise and movement.
4 There may be a more serious problem hiding in the upper part of the frame and head stock.
5 I assume that you have fully torqued 'all' the mounting bolts.
6 You will probably need to go over everything again with a fine 'tooth comb' and check thoroughly, here's a tip.
"When we repair anything thats been in a smash, it is very helpful to know exactly how and what type of impact was involved. Knowing this we then try to reverse the effects on the machine before too much dismantling takes place"
You probably have the first hand knowledge as you were riding the bike.
Bikes are much harder than cars, least ways a B#W is but the paralever and forks are the weak link at the front. These must be inspected extremely carefully as they can hide untold amounts of damage that could end up putting you at risk.
There, as I said diagnosing at a distance is difficult but I hope that you get the problem resolved.
