My 87 syncro has this strange vibration that comes and goes. My mechanic
is an excellent and honest one. the best explanation  he's found so far
is the fan belts seem to jump around alot like 1/2 inch or so when you
rev the engine up. It seems like a weird harmonic distortion thing??Open
for suggestions...........btw the drive shaft is out , we thought it was
the problembut it still has this vibration....

Rob Wilke
87 Syncro
78 & 77 saab
49 Chevy Pickup