Just had a universal cat. (back one) put on, on my 02 escape with 86000 miles on it. Had a tune up with new spark plugs and fuel system cleaner done while it was in the shop. A day after I got it home I noticed a rattle from the front, sounds like right under the driver side right behind the tire. Took it back to the shop and the guy wants to charge me $500 to look/ change the front cat. Said he didnt touch the front of the car last time so it isnt covered under the warranty. Any idea what the rattle could be?Sounds like it only does it at low speeds (may be b/c thats the only time i can hear it) This car is so frustrating.