50 hp yamaha noise and vibration

[ppidgursky]

I could really use some help here fellas.
When I start the motor she will run ok for a second or two then the noise comes. Almost sounds like gears or something metal rattling. The sound sounds the strongest on the left side, near the bottom of the motor. I removed the foot and checked the spines on the shaft...they are fine. I checked the oil in the foot it was low, and milky so I changed it. Still happening. If the foot was leaking oil, where would it leak from?
When I rev it up some, it clears up. Maybe 2-2500 rpms and up. This happens in and out of the water.
I rebuilt the motor not to long ago, and she was fine at first. The rebuild went smooth I guess. Everything put back together ok and smoothly. What could be wrong.. or do I need to tare it down again?

History:Motor is a Yamaha 1989 50ELF.
Have had the block bored 20 over, new pistons, rings, fuel pump, carbs rebuilt, new fuel lines, rebuilt water pump, new batteries, new gaskets and orings all the way around.

[jb123]

remove the lower unit, hook a hose to your water tube , run see if noise is still there, you said the noise is lower so probably need to repair lower unit and water can come in from prop shaft seal or seal under water pump.

[ppidgursky]

I'll try that today, and I'll get back to you. Thank you.

[ppidgursky]

Hello Again,
I removed the foot and hooked hose directly up to the water tube. Noise was still present. I was able to tune the carbs in some and got it where it does not do it as often, but will come and go. Once it starts, it is usually enough to basically stop the motor. She will spit and sputter and sometimes quit. If I give it gas before she quits, I can save it and keep it running.
Question: When I had the foot off, and I shut the motor, and water off, I noticed white foamy liquid coming from the exhaust port. I smelt it, and it had no noticable oder like gas etc. I also checked the spark plugs, and looking down the hole I noticed the top of the piston was wet, also on the end of the plugs. Unburnt fuel/oil... I don't know?
Would that mean the head gasket?

[jb123]

possible, check compression.