Got a van that's making a loud whine, more like a hoot, on deceleration. Does it in park and neutral, higher you rev it the longer the hoot. Drives fine, everything checks out on a scanner to my knowledge. Checked vacuum off tb and its good at 19, tried without rad cap and without oil fill cap. Does it with EGR hose unplugged.
Did notice on my vacuum gauge that the sound is consistent with vacuum, when vacuum goes up to 20-22 on deceleration, it hoots.
What do y'all think?

 

Oh, that is great, never heard that before. It actually does sound like an owl.

As-it-is, odds are it is the gasket that is between the TBI unit and the intake manifold. Easy to replace and inexpensive.

They usually cause a whistle sound at a steady idle. Once the gasket dries out it is common for them to make noise.

RBob.