Sounds like hooking up the Serp only increases the noise so now you know if it's something that's spinning which is left still spinning after removing the belt? The crank pulley. check for vacuum leak or pinched line. Grab a long screw driver and place it on non moving parts of the engine while holding it to your ear to narrow down the area it's coming from.
I think I'm onto something. Excessive crankcase vacuum? I let the car run for a while and took off the oil fill cap and got a WHOOSH airy sound (sucking or blowing sound). Also the car sounds like this when I shut it off. My oil fill tube to throttle body cable is kinked. I think it's preventing air from passing through.
Well I'm 99 percent sure its fixed. Just took her out for an hour with no oil filler to throttle body hose. No noise. So happy. I'll get a replacement hose from the hardware store.