1995 Plymouth Voyager AC grinding noise

I drive a 1995 plymouth voyager with about 167,000 miles. Recently when I've been driving it the AC will make an occasional grinding noise. The noise will go on for a second or two and then stop. It does this about every minute. What I find odd though is it only does this when I drive on the interstate going over 60mph. It doesn't make a noise when I start the vehicle or when I'm driving around the city, just on the interstate. Is this my AC compressor? What happens if this goes out? I'm uncertain if I want to fix it because I won't have this van much longer but I do need it to be drivable. Thanks.