The first time I got the oil changed (I've owned this car 4mos) the oil showed a quart low on the dipstick I got it changed checked it again they had filled it perfectly, I've been checking it every couple weeks and it showed no sign of going down I check it 2 days ago it's a quart low, I check it today it's lower. I get under the car there's no oil to be seen nothing on the top of the engine no puddles when I come out in the morning or after running it for a while. I've had my fiancee watch the car when I start it no smoke she's constantly driving behind me and never sees any smoke while i'm driving. The car doesn't run roughly it never hesitates to start the oil light has never gone on etc, is this something that happens with the altimas? Is there something else I should be looking into?