Hello Benz fans

I have had a ticking lifter that I intend to replace soon but I have a new noise. It sounds like a lifter but louder. It only seems to knock when I am on the throttle. At idle or coasting it goes away. I changed the oil to 10-40 over the weekend and although I don’t see any milky white, the coolant seems to be just slightly lower. The oil on the dipstick is bubbly. I drove 2 miles and it was very bubbly and after 12 miles it was less bubbly. I am not looking forward to pulling the heads. Anyone have any ideas?

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Steve
1985 Mercedes 500SL Euro (Gray market)
1995 BMW 520i Euro (Gray market)
1992 BMW 525it Wagon
1994 Honda Del Sol Si