loud squeal frome top of 2001 40hp merc

[walleye1968]

i have a 2001 40elpto mercury 2 stroke 2 cylinder outboard
s/n ot199135 it has a high pitched squeal that comes and goes
every 2-4 minutes from idle up to about 3000rpm
can hear it with the hood on or off in gear or nutural
cant pinpoint wher it comes from

thanks