http://www.subsim.com/radioroom/showthread.php?t=104377
If you haven't read this sticky thread by Ducimus then give it a minute.
It's really good and informing!
And according to that info and if it is based on real life they should realisticly have a small chance of hearing you in the situation you were in: three destroyers closing in from your port side scaning the area infront of the convoj, they are probably alerted since you sunk a carrier two hours earlier in the nearby area and you running at 200 metres around 100rpms and exposing your port side to the sonar.
Sounds realistic enough IMHO for a guy with small knowledge about ASW.
/Bracer