This 2000 crownvic has a buzzing sound on the highway coming from the windshield wiper cowl on the driver's side near the power brake booster and cruise control servo.

For some reason, most of the 2000 model year crownvics have half of the weather stripping under the windshield wipers missing. Here's a 1998 hood insulator next to the one from this 2000 crownvic

And here's a 1998 crownvic with a full sized hood bumper for comparison

And the 1998 crownvic with the half length 2000 hood bumper installed

Having half a hood insulator missing like this eliminates all downwards compression on the windshield wiper cowl from the hood. This allows part of the windshield wiper housing cowl to vibrate and make noise when you're on the highway with lots of air moving by this part

Sometimes, you'll find 1992+ crownvics with the entire hood bumper assembly missing like pictured below. This does not appear to be a problem with ford's manufacturing procedures, but rather a problem with a mechanic that rushed an intake manifold or windshield wiper motor repair job and forgot to reinstall parts.

Some 2000 model year crownvics are reported to have full length hood insulation that's split into two parts. But the vast majority of pre-owned 2000 crownvics that you'll find will be missing the driver's side portion of the insulation.

The service part number for new hood insulation: F2AZ-16740-A. This part is listed as fitting all 1992-2010 crownvics in service parts literature.