On 01/16/2016 5:41 PM, DerbyDad03 wrote: ...
It does seem a little short but much would have to do with the actual conditions in the house as far as evaporation rate and what the actual trap design is; they're various shapes and mayhaps this one is "more flatter" than others. It's also possible there's some suction being applied owing to venting but my bet would it's not the issue and might as well eliminate the quickie, easy as the culprit first.
As for the question; not here, no, we don't in specfic. There was one in the basement in the house in VA but it was a floor drain with full 2" drain so the size of the trap was quite large compared to a fixture drain so no comparison.
I'd still posit as my best guess it'd behaved the same way while the house was occupied if the shower (and probably a shared lavatory?) were _never_ touched but that it didn't occur owing to there being the occasional use or even just routine cleaning, etc., that would freshen the trap without your even thinking of it or recalling that such did happen now as it was so routine.
But, yes it is possible there's a new phenomenon altho I'd really be hard pressed to think of something outside the house; there being a blocked vent from a bird nesting or somesuch would be higher on my list than that (see above)...
Good luck...