Hi,
Well... it seems i am that friend that lior (i3dm) is talking about.
as for balancing, i was thinking of using the method described by WREN at their kit manuals - jut put the shaft with the compressor in a specially made cylinder (that holds the bearings) and rock it around on the table's edge...
find the "heavy side" and grind off some weight ... repeat until satisfied.
then redo it all with the turbine wheel.

but yet, the questions remains -
are there any distinct noises or behaviors that indicates the bearings are reaching their end?
if it is a balance issue, what could cause the turbine to "spin out of balance" ?

thanks.
Ravivos.