Yep bubble trails wake em up real quick in broad daylight
example: during the Norway campaign there's a stationary British taskforce in a fjord, 3 DDs a Fiji CL and 3 juicy troop transports, I'd used my electrics to take out the DDs they never knew what hit them, so there was the Fiji that moved a bit but stopped again after all the Escorts went kerblooie, I fired 2 steamers at the Fiji, the weather was flat calm and broad daylight for this (I wasn't going to wait for the luftwaffe to steal my credit) It spots my eels I guess about 750 meters out, it immediately steps on the throttle, goes to 12 knots and the fish pass well astern
so yes they do notice and the lighter, more turnable ships ususally manage to evade