i need some advice about a 91 civic.
 

im thinking of buying a 91 honda civix dx that i found e-tested and certified for very very cheap from this guy who needs money badly... the only thing that i noticed while test driving it was that when i accelerated , the car would make a kind of buzzing noise and would continue until the car came to a stop. it seems like the sound is coming from somewhere under the car. also when i stopped at trafic lights, the car would run heavy and rattle but as soon as i fed the car a tiny bit more gas, it sounded smooth and stopped rattling.... the car has a total of 270.000 km on it and has a 4 cyl 1.6 engine with 120,000 km on it. what do you think is wrong with this car? why does it buzz and rattle? ....in general, how much would it cost to repair it? . any opinions are appreciated.