I once had a similar sound, it was when the car was cold, but heres the kicker....it did it simply when I turned the ignition on, even when the car wasn't ruining. I doesn't do it anymore, but I really wonder what the hell it could have been. I'm pretty sure that it was coming from somewhere in the engine bay, but it doesn't do it anymore, and I can't remember when it stopped, but it could have been when I got a new ecu. Anyone know what the sound is from?
Also, I kinda compare the sound to like an old computer's noise. Like when its under a lot of load and makes kinda clicking noise, only mine was more like a grinding noise.