Any detectives out there who can spot what might be causing this? This is just one of about five lagers I've tried, some with different yeast, and they've all had acetaldehyde. I am at my wits end.
Sounds like oxidation to me. I'd check o2 exposure when cold crashing in regards to suck back. Also, when kegging - do a closed transfer if you can. If you can't, purge the keg with co2, then siphon in the beer (with the lid open) while pushing co2 in the gas post at a very low psi - close it up, and purge 3 more times.