Make another recording at an exact speed and tell me the speed.

I can determine if it's drive train or not with some meausuring and math.

Not long ago I determined a similar mystery sound was exactly 3x wheel rpm which led to thinking CV axle (inner joint has three lobes).

If we can find a part that rotates at a similar rate it may determine the source.

Do you have any universal joints or just guibo? A recent thread showed a u-joint disaster that grenaded and blew out the side of the block. We want to rule that possibility out before it happens to you