New noise

I have a 2008 Z4 3.0 Si Coupe. When I get on the gas winding through an on-ramp, I am hearing a brief "whuuup" as it up-shifts through each gear. It will occasionally do it off the line but I usually notice in accelerating sweepers. It almost sounds like a smooth pop-off valve on the up-shift. Something to be concerned about?



I go off of the extended warranty in May and would like it resolved on BMW's nickel if it's a problem. Only 43,000 on the car, not tracked.



TIA