New owner of a 2009 Sonata with a question
 

Bought the 2009 Sonata GLS on Jan 6, 2009 and already have 7800+ miles on it. Very happy with gas mileage. Drove it over 2100 miles from AZ to MI and averaged 38 mpg with one tank of 43.3. Lowest was 33+. There is thumping in the rear. I'm wondering if this is what the sticky is referring to and if the sticky applies to the '09s. Or could it be because the car is a GLS and has less sound deadening material than the more upscale models? Thanks for your replies.