I'm dealing with the same thing right now - took a Jeep Compass with 30k miles on it back after the check engine light came on the second day I had it - don't think I drove it 30 miles. To replace that they gave me a Nissan Versa with 40k on it that made horrible knocking noises for two days till this morning when the gas cap warning light came on. Pulled over to look at it and the gas cap is 100% broken - as in impossible to screw on. I'm really annoyed that they rented me a car that someone at Hertz had to have known was broken. I'm lucky that I'm not far from the airport location but don't really want to deal with this today.