duba-duba-duba-duba ...

Or is it pop-pop-pop-pop ... ?

Or maybe glug-glug-glug-glug ... ?

The typical scenario where it's the most obvious and easily heard: I'm driving around 60 and slowly decelerating, e.g. "coasting" as I take a freeway off-ramp. There's a fairly loud, distinctive pulsing drone that can only be described as a "motorboat idling" coming from the *front* of the car. Relatively high pitch, but only around 5 cycles per second. Brakes are not being applied. Tires appear OK. Steering wheel is not vibrating. Passengers are looking at me funny.

Hmm.

--Brad