We just got the oil changed and two new front tires put on a 2001 Freelander. The day after this work was done, I noticed that the car was making a odd noise at higher speeds...kinda like a deep rumbling noise. This made acceleration a problem for me. The day after that, I noticed an odd odor inside the car that smelled exatly like natural gas from a stove.....No smell from under the hood, just the inside of the car.

Any thoughts?

 

I wouldn't wait around for us to guess, you have a problem and I would suggest either you pull off the new tires and do an inspection or go back to the shop that did it and have them check. Also, make sure you are not leaking oil that is then being burned off on the exhaust.
Mike