Hmm i tried it right now and it seems its only once, thats ok for me, thanks!
BTW i really love DD's hunting AI, its really fun to fight with their tries to find you by some searching pattern and so...
Especially funny when he tries to shut down engines repeatedly to hear yours 
Sometimes it seems to me they learn from my tricks which i try to escape from them.
Once i hanged after one DD and kept his tail for about minute in hard turn left, then just select rudder zero, i let ahead flank for a while as i was still behind him and then just all stop....
I ran just by inertia for very long time, much quicker, than at small speeds and without any sound.
After some his searching he heard me again because as i found, they can hear even 3.rd speed level even from long distance.
You can run at flank ahead even very close if you're behind him and he has engine on relatively faster, but since he is on "constant distance" course, i always switch 1. speed level..