I don’t believe that the water that drips from condensation tube for the AC is enough to rust out the engine craddle/subframe. First, the amount of water it see’s isn’t constant from that area. Second, that water is driven off from heat and air movement as the vehicle is moving. And third. If that small amount of water caused that much damage, then there should be engines/transaxles falling out of 2000 Accords here in Minnesota where they use salt on the roadways each winter.
What you were told is causing the noise sounds pretty fishy to me. Get a second opinion.
Tester