Coolant smell at WOT

[Luk4shO]

Hi all. I have an weird issue with my second M5. It has 66k miles on the clock, recently serviced and new coil pack installed. However, it developed an coolant smell when I push it hard. I can only smell it if I crack the window open so I don't think it's coming from the vents etc. I checked the turbo lines and can't see any leaks there, although one of them does seem swallen. Checked the turbo coolant level and it's fine, sitting at max. Can't check the engine coolant level as there is no easy way to do so. Oil cap looks ok, no milky residue, car doesn't smoke and the exhaust smell is fine at idle. It's only when I punch it to about 5000rpm or above when I can immidiately smell it with the window open. I'm kinda hoping it's them turbo coolant lines but can't see any evidence. Unless it's so little it vaporises instantly by the time I get there to check. Engine running otherwise perfect, no wonky idle, pulls nicely etc. I read somewhere about charge coolers leaking coolant into turbos or turbo coolant seals leaking but that was not on F10 M5's. Any ideas?