Getting nowhere..need some help please

OK, so my wife's 2005 X3 140,000 has a clicking sound underneath, I was on the actuator trail, but no lights on the dash and I listened to a video earlier of a bad actuator. The clicking of the bad actuator sounded somewhat like trying to start a car with a bad battery. That is not what ours sounds like, our sound is a clicking that goes along with the wheels rolling. The faster they roll, the faster the clicking, the slower they roll, the slower the clicking.
It's like putting a card on your bicycle spokes (remember doing that)? I can't tell where it is coming from, I thought that it might have something to do with a brake caliber?
I took it to an independent garage, he thought I should take it to a BMW$$ store, and that the noise may be coming from the Transfer case, that it did it when the driveshaft was turning.
I am stumped and am looking for your thoughts. Thanks ever so much !

Can you open the fill plug at the top of the transfer case and confirm that there is fluid in the transfer case? Does it not make the noise when you are standing still?

Thanks for your response. The noise stops when standing still, the faster you drive the faster the clicking, the slower you drive the slower the clicking,.

Have a shop put the car in the air and drive it. You can then find the noise.

Do you know if the mechanic checked the rear wheel bearing?

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I hope you have a stone stuck on a tire that causes the clicking sound while driving.

Anything else can be expensive to repair.

Check:
Front and rear Diffs.
Transfer case
Wheel barrings (all round)
Belts (aux)

Nothing else can "click" as fast as you are driving.

Go to your mechanic again and drive the car while on the lift to see wtf is going on.

Talked to the shop again today. They put it in the air, took off shields, said noise seemed to be coming from transfer cse area.