cad 390 engine noise, what could it be???

[eugene]

I have a61 deville with a 390.  Lately it has started making a intermitent high pitched whine.  The oil light is off and pressure seems good.  It doesnt start making the noise until it is warmed up.  It tends to make the noise more at idle than at higher rpms.  once it makes the noise I can rev the motor and it will go away for a minute or 2 but comes right back.  I layed under the car with it running and it sounds like its coming from the back of the oil pan.I put a stethascope to the back of the pan but didnt hear anything abnormal, however the noise is definatley the loudest when your under the car.  A local mechanic told me that it could be the oil pump.  A buddy of mine thinks it spun a main bearing but I think if it had spun a bearing you would hear the noise all the time.   The car runs nice and smooth it just makes this noise.  what could this be?

[Dan LeBlanc]

Maybe the noise is coming from the transmission?  Perhaps the pump?

[eugene]

it ended up being a vacuum leak at the back of the intake manifold.

[Dan LeBlanc]

Gotta love it when it's a simple fix.