new top end squeek

just got the new top end on and im breaking her in. the only thing i noticed was a sharp squeek when the bike is idling and when i let off the throttle. the sound is only for a split second and goes away. it scared the bejesus out of me so i shut it off immediately. i made sure that the piston rings where in the correct place and that the piston/cylinder was well lubed. i also made sure to manually move the piston up and down the cylinder before puting the heads back on. there was no scratching noise there so this is why im worried. any ideas? im going to take the heads off and check the piston and cylinder again then retorque the heads on.

cheers
hely

74 Yamaha RD350 cafe