Hi. I have the same problem.
Look here:
http://www.subsim.com/phpBB/viewtopi...hlight=#324203

If you can't speed the time compression up past 32X, I'm guessing there's probably another unit (ship, sub, or aircraft) in the general vicinity. If you're on the surface, and time compression slows down, submerge and go quiet, and have a listen on the sonar. If you still don't hear anything, it's probably an aircraft that came close, but not close enough for your radar to pick it up.

I could be wrong, but most times I have problems with the time comrpession, this is usually the case.

Remember, even the trip home is supposed to be realistic. In the campaign mode, you're likely to encounter more traffic on your return leg, and if you're out of torpedos, the objective is to evade without detection.

Cheers.