Why is my espresso salty? We've got a fancy espresso machine in our office kitchen. (It's apparently the kind they used to use at Starbucks stores before they switched over to a more automated "point-and-click" type system.) I was trained on how to use the machine by an old pro, and have been successfully making delicious cups of espresso for a few months. 

Lately, my espresso tastes distinctly salty. 

I haven't changed the process at all. It has happened on a few separate days, with many other people using the machine, so I doubt it is an issue related to the substance used for cleaning the machine (since I believe that would have been flushed out between my attempts). I haven't heard any other complaints from the 50 (or so) other people who use the same beans, grinder, and espresso machine. 

It's a mystery to me, but salty coffee is gross, so it's a mystery that needs solving. (My theory is that I've unwittingly altered my method in some tiny way that I haven't noticed, and that has changed the taste of my espresso. I just don't know what that alteration was!)

Edit: I had a thought: This morning, I made a cup that was salty enough that I didn't want to drink it at all. I poured it out and made another from the other basket on the same machine. It was salty, but drinkable. Potential clue?

'nother edit: Yesterday, my coffee was less salty. The only difference in my method was that I rinsed the basket for way longer than I usually do. It still tasted a little bit off (in the salty direction), but not nearly as bad as previous cups.
It could simply be that it's a gustatory illusion!  See my answer to this related question for more explanation.

Edit:

Here is a summary of the relevant information (if you don't want to follow the links):

Human taste receptors don't simply react to how much actual salt there is in a food or drink; our perceived tastes are a fusion of both our gustatory and olfactory senses.  In other words, the smell of a food or drink can affect how it tastes!

There are numerous studies that suggest foods with certain odors can be perceived as much saltier than they actually are.  Coffee has a good amount of oil, there's even more fat if you add cream, and other studies suggest that high fat foods can also increase perceived saltiness.