'98 Riv startup noise???

Second thread on this...originally thought my startup noise was supercharger. Disconnected belt on s/c and engine still sounds like bad-like it's coming apart...some bearing? Weird metallic noise? After a few minutes the noise goes away and everything sounds fine. Not lifter noise, my mechanic friend says it's the "cold air" entering the engine thru the supercharger ports and when air is warmer and mixture is different that's what makes the noise leave. (I'm finding this very hard to believe) Engine runs strong, have KN cone filter on it, has 65,000 miles on it. Runs so smoothly you could probably balance a coin on it at idle. With s/c on it reacts immediately like "a rocket".
Any thoughts or suggestions would be greatly appreciated. thanx...t.r
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While the engine is cold, try disconnecting both belts, then run the engine for a short time before it overheats. You'll at least be able to isolate the noise to either the internal or external part of the engine.