Just as a safety check, I would check the water pump pulley for play indicating the seal/bearing has given out letting the impeller “spin against“ trying to shave the block inside. I had the exact metallic sound from one of my 740is and that’s what it was, the belt tension prevented the pulley from shifting while it was running so I didn’t see the pat until I pulled the s-belt. After pulling the pump, luckily I had caught It early, but it still was beginning to wear a groove into the block wall behind the impeller...
Just as a safety check, I would check the water pump pulley for play indicating the seal/bearing has given out letting the impeller “spin against“ trying to shave the block inside. I had the exact metallic sound from one of my 740is and that’s what it was, the belt tension prevented the pulley from shifting while it was running so I didn’t see the pat until I pulled the s-belt. After pulling the pump, luckily I had caught It early, but it still was beginning to wear a groove into the block wall behind the impeller...
Thanks for the replay buddy, it ended up being the alternator which was going bad.
Lucky break on that one, just wanted to give you another base to check in case, glad to hear you found it...