Rattling noise in front?

[GTRS Fiero]

After running through some twisties, my Fiero developed some new noises.  I cannot identify a noise from the front.  This particular noise sounds almost like a phone on vibrate, then shuts off like a faucet.  I cannot determine where in the front this noise comes from.  The noise continued on smooth, flat, straight highway.

I do know that the noise is not rotational.  The noise is of varying durations.  It could possibly be in the left front.  The noise is not the blower motor, nor does it appear to be a gauge motor.  The brakes still operate normally.  No wipers or washers were being used.  Nothing with the engine or vehicle behavior seems to be affected.

What could the noise be?

[Raydar]

Could it be the air diverter / temperature control doors in the HVAC system? They're motor operated.

[GTRS Fiero]

Well, it did this with the HVAC off, as well.  It didn't sound like that, though; it sounded like a phone vibrating.

[TopNotch]

Have you checked to see if you still have your phone?

[GTRS Fiero]

Actually, yes.  My phone was on the seat.  I held it in my hand for a bit, anyway.  Not my phone.

Not April Fools' Day, either.