I am the peptide master!
It turned out to be a series of adducts that shows up when you have a certain component in your mobile phase and a certain set of residues in your peptide, and only on certain instruments apparently, because it used to be fine on the machine in my old lab. The only way I could figure it out for sure was by making this crazy spreadsheet of all the possible adduct combos and charge state series that went with them, and finally found the matching patterns in there for every single peptide we've had the problem with.
In other news, I am sleeping at the lab tonight: husband is out of town for work, roads are icy and treacherous, no point in making a dangerous, slow (2h each way in these conditions) commute when there's nobody to go home to. I have my Ikea pull-out couchbed and a change of clothes, and I am rocking it total nerd style in my office!
So far it has been pretty awesome to actually be able to get a ton of shit DONE because of being on my own for a good solid five hours. Things such as SOLVE THE PEPTIDE MYSTERY now that there aren't any pesky kids around lab! (just kidding for Scooby-Doo effect--I love my labkids, they are all wonderful)