You answered your own question. Also, you may have an overfilled oil situation. Store your bike on a wheel chock that will keep it straight upright then you shouldn't have that oil pooling problem into the left cylinder.
I had the same problem. The Service Bulletin solved the noise. Call you dealer and ask the service dept. to look up.
BMW R18
PUMA - Service Bulletin
S1 13 07 21
Loud / Noisy Fuel Pump
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