Mystery sound - e-box related?

[blazenXLT]

Ok, this has been driving me crazy... quick background, I drove the M3 2 weeks ago, it started right up no problems. Drove about 20 minutes, made a stop, 20 minutes home. Again, no issues on start-up or driving. Two days later I went to get something from the trunk it the battery was dead. Strange, but not a big concern, I hooked up the charger. About two hours later I came back to the garage and there was a fan-like sound coming from engine compartment, near the driver's side by the brake fluid reservoir. Not a sound I ever recall hearing before.

I know there's an electronics box fan, but I've never heard it like this, and didn't think it should run at all when the car is totally cold. I disconnected the charger since I didn't want anything running full time. It dawned on me to check the battery and it was from 2015 - not sure how I didn't realize it was that old, but oh well, I figured that was the problem - battery is spent and maybe won't take a charge at all. A few days ago I picked up a replacement battery. As soon as it was hooked up, the fan sound started again.

I'll spare typing out everything, but I've gone through testing by pulling the SAP relay, pulled the fuse for the e-box fan, pulled the fuse of the HVAC/blower motor - sounds keeps going. What am I missing?

Here a quick clip - https://youtube.com/shorts/XS3fS5Grx...5kEafhZAbcxyk-

[sapote]

check if the heater control valve is warm or hot to the touch. Pull the cable off if valve is hot/warm. What fuse you pulled for the efan?

The mystery thing drained the batt.