Whining 96 Voyager 3.3l

As of recent days, a loud whine emits from under the hood. Put it up on ramps to hear what I could hear. Using a stethescope (long screwdriver) I found the area that the sound seems to be generating from. It's where the oil dipstick/oil filter are attached. Could this be the oil pump? Bad filter? Changed oil not to long ago. It happens when vehicle warming up to operating temperature, then goes away. It's not coming from transmission. Just had it rebuilt and operates fine. Proud to say first tranny replacement at 156k miles!

Thanks.

Update on previous post. Performed an engine flush. Dropped oil pan. Needed a new gasket anyway (leaking), inspected pickup tube and screen. Replaced with new pan gasket, and o-ring (pickup tube to oil pump). Changed filter and oil. Nothing remarkable from below. Problem gone.