noises from transmission clunking

I own a bmw x3 and the transmission has started clunking and at slow speeds it feels like a lump in the driveline when coasting slowly.!! It can be intermittant. Also at about 35 40 mph it a very slight humming appears. It is not a wheel bearing.

What year, mileage, type of transmission A/T, M/T?

Can't tell from the description but some X3's (maybe all, it's impossible to tell) shift roughly to the point that the car will suddenly decelerate or jerk back and forth at low speeds. Some people think that it is the s/w programming (either deliberate or defective - who knows?) but that doesn't make much sense as others say it is worse in cold weather which sounds like a mechanical problem. Who knows, may it is the programming and a mechanical problem exacerbating the s/w problem.

I don't know. I don't think anyone else does either as no one can explain how a s/w program alone gets worse in lower ambient temperatures.

Some people call it the sling shot effect during acceleration and pulling back during deceleration. I think it is poor shifting that can be so sudden and hard that if you get the downshift unexpectedly just as you are braking then you get a hard stop.

I also think the shifting problems also cause intermittent power surges. When moving along at moderate speeds, there is a sudden (intermittent and unexpected) surge of power for no reason. I think that may also be the transmission shifting oddly.

Why it does these things, no one but BMW knows for sure. I'm just speculating as to the cause of the symptoms that I personally see.