I have a 2004 Mazda 3 (stick) with 140K miles on it. 2 problems.

PROBLEM 1 - OIL USAGE -- Switched to Mobil 1 synthetic on the last oil change and my car uses oil like crazy. I check my oil every week and its always low...added 2 quarts last week. No leaks or smoking. Car runs fine. Read someplace that i need to use a synthetic blend. Anyone have any thoughts on this or can u send me to a link for this discussion.

PROBLEM 2 - Car rumbles when I coast (no foot on gas petal) or I press clutch pedal.
The sound sounds like a engine rev but RPMs stay the same. Acceleration car sounds normal. Replaced motor mounts (all) at 100K. Any thoughts...