Engine smokes once in a while?

once in a while while im driving my subaru outback smokes.. it usually comes from the axel and only occurs whill ime driving it smells like rubber burning.. i think it might be the power steering.. u think i have to get it fixed right away? it smokes about once every 10 drives and it stinks. i just got an oil change.. o yea my car always has low gas so idk if that s the problem. the car is slower than usual + it has 155,000+miles.. please answer if u had this problem and tell me how much it cost u