my 2003 Roadstar 1600 runs great.
When the engine is cold and been sitting for a week or two it will make a weird sound in the first minute or so of the engine running and then goes away. Sounds like someone is in there lightly tapping on a hollow metal pipe with a ball peen hammer or something similar to the sound a hot exhaust pipe makes when you first shut the engine off after riding it a long time and everything is heated up.
The bike only does this intermittently and only does it cold start after a week or two of inactivity. Never makes the noise again during the same day regardless of how many times it is re-started or if the motor is cranked multiple days in a row.
This occurs when I do a cold start with the enricher cable pulled out a bit and the bike in neutral resting on the side stand.
A bud who is a long time Roadstar 1600 owner heard it one morning and was asking me what was the source of that noise. His 2001 Midnight 1600 does not do that. Both of us have similar mileage in the low 20Ks and both of us are running Mobil 1 20W50 synthetic with Yamaha OEM filters.
The bike had V&H
longshots on there when I bought it and one could not hear this sound above the volume of the pipes. I like quiet bikes and installed stock exhaust not long after purchasing the bike and that is when I first noticed the cold start noise.
I put about 5K miles on it since changing back to stock exhaust and no variation in engine performance etc.