Lincoln/Mercury: 1999 Infinity G20 - grinding noise, excessive tire wear, o2 sensors, infinity g20

Question
I had the front end realigned in March and front tires replaced 2 days later. Now, I hear a grinding noise that occurs about every 20 - 30 seconds, stops, and then starts again. The new tires are excessively worn on the outside edge and the "service engine light soon" comes on for a few days, then shuts off and comes back on.

The repair shop says the front end needs to be realinged again but they think the same thing will happen and do not know what is causing the tire wear.

Help! Please.
Heidi  

Answer
Heidi:acording to my service manager,the tires may require a four wheel alignment or wheel bearing may be bad. the tires could also be "cupped".may I suggest get second opinion. the service light could be from loose gas cap or o2 sensors(emissions).one more thing-if repairs become too excessive,consider other car,perhaps a new sentra. good luck!