[E92Stock335i]

Hey Everyone,

New here and my first post so please go easy. A month ago a coworker noticed that there was some blue smoke from the exhaust at startup and yesterday I noticed that after downshifting from fourth to third and really stepping on it I saw some smoke from the rearview. After inspecting the exhaust in the morning at startup, I notice a brief puff of smoke which looks more grayish/blackish to me then blue at all. After I start the car there's a brief moment before the smoke comes out a short rattle from the exhaust and then the smoke from the right exhaust. Today after i got home from work I had a friend rev the engine before I shut the car off and only about after the tenth time did I see a small puff of grayish/blackish smoke from the left exhaust. Any ideas that point to one thing based on the evidence? Some facts on the car-2007 335i 6MT coupe completely stock. Just ticked over 146k miles thanks to my 90 mile round trip commute for the past three years. Got the car in 07 with 10k miles on it. I've had the spark plugs changed about 15k miles ago as well as the water pump and thermostat. Oil filter housing gasket and "intercooler tube o-ring" about 25k miles ago. Oil changes every 5k miles since ticking over 100k and sometimes I need to add a quart just before I reach the next oil change and sometimes I don't. Was averaging 26.1mpg before recently dropping to 25.8 this summer. My commute is mostly highway miles with a mix of cruise control at 75 mph and some spirited passing and on-ramp fun. Car has had turbos replaced due to wastegate rattle, HPFP replaced twice and fuel injectors replaced while it was under CPO warranty. Might I also add the car runs great! Still pulls strong and has been reliable since all those major repairs from the dealer. From my searches here I plan to have the following preventative maintenance that have never been done at my next oil change and again just looking for some feedback: valve cover gasket, serpentine belt, walnut shell blasting intake valves, RB pcv-valve and cap. Anything else you guys would recommend they do while they have it relative to the smoke issue or even just in general? I must apologize for the novel I just wrote but wanted to provide all the relevant information that I could think of. Thanks in advance!