Oil burning smell plus 'check oil level' warning message.

[alpac]

In the last few days after driving on highway for a little while I have noticed a oil burning smell and smoke coming from somewhere underneath the back of the engine and the 'check oil level' warning message from time to time when I turn off the engine. The valve cover gaskets have been changed 9k miles ago and the oil breather 12k miles ago so it is not that for sure. This is a 4.4 with 90k on it. It is still under extended warranty but I usually try to figure out what the problem is before bringing it to the dealer so I can tell them what to look for.
One thing I have been thinking about was the oil separator lines. Did anybody experienced such smell and smoke?
Thanks