Loud buzzing noise while accelerating?

Really confused… I have a 99 VW Passat, it is making a loud buzzing noise as I accelerate to speeds above 20-25mph. The noise sounds like a baseball card in your bike spokes (or a room fan) does. The noise disappears when I push the clutch in. Here’s the really weird part: when revving the engine as it’s parked in neutral, there’s no sound.

What the heck is going on?

Maybe exhaust system…crawl under, and with a gloved fist, pound on all the parts of the exhaust you can reach.

The noise might be from a buzzing heat shield on the exhaust system.

Heat shields can make a buzzing noise when the engine reaches a certain frequency or hertz.


Interesting… so when hit it should rattle or be loose? Thanks.