Had a similar problem...

Change the pre-cat O2 sensors and the spark plugs.

How is your Heat & A/C blower motor doing? Might be source of the buzzing sound?

__________________
'07 e83 x3
'91 e30 325i



BMWCCA Member... 20% off BMW Parts, 10% off BMW Labor... best $50 / year you'll ever spend!