My current patrol has me assigned to the Philippine Sea and the convoys have started using escorts - mid-'42. I'll get my share of DC's soon enough.
On my last patrol I had two destroyers looking for me, but I never heard them use active sonar. I went to test depth as soon as I fired my three fish at a freighter and ordered silent running. I was passed over twice, but they never pinged me or dropped any cans. They stayed in the area for a few hours before moving on.