My 06 Vantage Coupe has started making a very strange noise.

I have attached a recording of the noise. In this clip I am coasting downhill in neutral with the engine running. The HVAC fan is off. The noise speeds up with vehicle speed (yet engine and gearbox speed are constant). It seems to be coming from somewhere around the driver's side dashboard.

Curiously, around 22 seconds there is a "clunk", and the noise stops. It did not start again for the remainder of the drive so maybe it's gone, but I would still like to know what it is/was.

Any ideas?

 

maybe a rock in your rim?

or possibly a resonant vibration from something in the glove box

 

That's about the only thing I can think of that would increase in speed with vehicle speed, while engine/gearbox speed stays constant.

 

I had something similar but louder, scared the hell out of me. Was making a turn at a traffic signal and all of a sudden a rattling, I thought the driveshaft was coming apart. Slowly limped it around the block back home and as soon as I turned into the garage it suddenly stopped. I inspected everything but could never find the culprit. I suspect some sort of debris in the wheel, maybe hitting the brake caliper.