1999 5.7 with sx m outdrive ticking/knocking under load

[55flybyu]

I just purchased this boat friday took it out sunday. Started and ran fine for first hour my daughter decided she wanted to tube..she tubed for 10 minutes and fell off we slowed to pick her up and allow her to get back on....when we went to take off again the engine compartment had a clicking/knocking noise while under a load seemed to be coming from the rear area... Stopped put in neutral and no noise at all as i reved up the engine..put it back into gear to take off and ticking noise came back and increased as rpms increased
Oil pressure good, temp good...
Pulled in the tube and took off to full speed clicking sound still there but motor ran fine no loss of power. No hesitation
Got home with muffs on could not reproduce sound while in gear or neutral, used stethoscope on engine area purred like a kitten
Any ideas please help, thanks in advance

 

[rossbuilders2004]

The exact same thing is happening to me right now, I can only get the ticking noise to happen in gear under load, on muffs or in neutral you can give it 4000 rpms and nothing happens, runs like a champ.