This popping sound occurs when trimming down as engine strikes trim rods and they begin to compress rod into cylinder. Noticed when checking PTP measurement yesterday. This is new and I hadn't heard it until yesterday. Seems like it’s the port trim rod area. What could this be and what should I check? I’ve fully extended and compressed rods and it still continues. I don’t see where the nearest grease fitting has any thing to do with this movement. Any ideas?