I just bought a car from a private party for around 7K and only after driving it away (and sinking 1.5K into other repairs) did I find that it makes a loud whining noise above 40 MPH (didn't do any high speed test driving). The dealership diagnosed it as transmission that is about to fail to the tune of 6500!!! Dealership said there's no way this person didn't know this was a problem. Mass law states: "If you discover a defect that impairs the vehicle’s safety or substantially impairs the use, and can prove that the seller knew about the defect but failed to disclose it, you may cancel the sale within thirty days of purchase." It seems the seller had to have known of this noise (and there is rattling at 65-70 MPH). Is that and dealer saying he had to have known enough to make a case?