The stock wide lobe separation is for the restricted exhaust. The reversion from the tight pipe would just negate any scavenge from having an overlap period. Also why a open pipe doesn't add much power with stock cams. The short duration and slow ramps, even with mcm timing, there is very little overlap at 1mm lift timing. The torque you feel from the mcm timing is mostly from the change in the intake closing time. Closes earlier so the dynamic compression is raised, with a compromise of less fill at higher rpms.

 

It is the fuel pump it is very noisy on most W800. You will first hear it when you turn on the motor to pressurerize the system, then it stops, after starting it it will run constantly, that's the sound you are hearing.

 

Good call Raymondo, the fuel pump noise would make sense, although really annoying for sure.