Thanks for many good suggestions! I came to my boat to inspect more, but will not start it now as it appears that there is again plenty of diesel in oil! The oil level has risen quite a lot from where I filled it yesterday, and oil viscosity seems to be very thin. Maybe there is also some other leak in addition to injection pump (which had definitely previously leaked, and should not leak now). Could this also explain the noise?
Just to clarify: the previous problem I had was with injection pump, not the fuel lift pump, which also has been replaced couple of years ago.