I have a BMC filter fitted to the M3, defo increases induction roar to a nice meaty level without being intrusive. Only really noticeable when you really dog it
I have just purchased a BMC cleaning kit which comprises the cleaning solution and regeneration fluid.
1: Shake filter to remove larger dirt particles if any
2: Sprinkle the BMC detergent onto the filter and leave for 10 mins
3: Wash filter in cold water - rinse well ensuring dirt does not enter pleats
4: Let filter dry naturally
5: To oil spray the surface lightly from 15cm away
6: Allow filter to absorb oil for 30 mins and then wipe to remove any surplus oil
Mine has been in for about 4,000 miles but BMC recommend 10,000 miles I think.
I will save money next service as BMW won't have to change the air filter