| Thats pretty steep for a software upgrade only. Average should be around 3-400 tops.
If you swapped the M-ASK (radio) already then the next 2 most common culprits would be the amplifier or the TCU (telematics control unit.) If you just disconnected the AMP and left the fiber optic lines just hanging there then that could cause noises on its own due to the light attenuation. What you really need to do is jump the fiber optic leads at the module so that the light is fed to the next module and therefore you are essentially bypassing the module. This can be done using a "MOST BUS" optical jumper which you can buy from any BMW parts department. If you have been reading on all the forums as you mentioned then you should be familiar at least somewhat with MOST BUS by now. All of your entertainment modules are basically "looped" together in series in a fiber optic ring known as MOST BUS. Popping noises are usually due to light attentuation on the MOST BUS. This can be from lots of things but most of the time its due to a failing module which is pulling the light signal down. As I mentioned before if you have eliminated the M-ASK then the next most common 2 would be the AMP and the TCU then you could go from there depending on your equipment level. If the TCU is failing then your dealership can give you the option of coding it out of the system to save you the replacement cost. Irregardless of what it needs if you are out of Factory warranty then any coding or repairs can quickly get very pricey. If you do replace any modules yourself keep in mind that they MUST be coded to the vehicle by a dealer. Also keep in mind that most used modules can not be fitted to another car and coded because they are already married to the original vehicle that they were installed in. Hopefully some of this info helps. | 
