Did you smell the old lines when you pulled them? OK, you know you did... How did they smell?
And did you smell the new lines? Any strange odors??
~Feel your emotions, but control your behavior~ Unknown
How old is the water heater? Maybe the anode is bad and letting a chemical reaction happen in the water that is going to the high point in the system, (upstairs). Seems strange it would just start happening now though.
Just another reason I hate plumbing!
Newish hot water heater, 3years, and it definitely isn't the hot water anyway.
Right now, after replacing just the supply lines, there is no smell. But the old supply lines didn't smell. We'll see what the next few months bring.
I'm beginning to hate plumbing,too. Do I mention the outside manifold for the hose broke in the midst of all this? Oy Gevalt!