I think the really telling part of this is that it is a recent development. So I'm going to guess that it is not altitude, unless your elevation has changed recently :). I'm also going to say that it isn't that your beans are too fresh, as you clearly aren't taking any chances there.
Let's get some more info, if we could...
How fast are your shots pulling?
Any variation in time, good to bad?
How do the frothy shots taste?
What are you using for machine cleaner? how often? do you rinse thoroughly?
When was the last time your water softener/filter was changed?
Do you pull into shotglasses or into the cup? (thinking possible soap residue on the cups)
As an aside, you may want to review your stocking plan if you are using 1 month old espresso. This strikes me as being pretty old. I know we have crema problems (going flat quickly) with older coffee, meaning the other side of 2 weeks, which is a very rare occurrence for us. Also, is the age a guess, or is your inventory dated?
Looking forward to your replies so we can help you more...