Alternator or alternator pulley by any chance?
I have the same symptom. I had been thinking it was the clutch or flywheel, it sounded like loose bolts floating around. I finally got a new clutch and flywheel installed about 6 weeks ago, throwout bearing replaced too of course, but the sound is still there.
Last week on a hunch, I checked the idle voltage with a multimeter. It was fluctuating in the low to mid 13's and the fluctuations seemed to coincide with the rattle. Above 1,500 rpm's or so the rattle goes away and the voltage stays dead flat.
Is this enough evidence to buy a new alternator? Also, the voltage reading at a 3,000 rpm's was 13.9 and low 13's at idle. Is this normal or a little on the low side? I have an under-drive pulley installed. Below is a link to an alternator I have short-listed. Thoughts??
New Porsche 911 Boxster s H6 Alternator 120A 97 04 M T | eBay