1993 Nissan Sentra Car makes very loud motorcycle noise?

I have a 1993 manual Nissan sentra with 190,000 miles on it. I bought it from a man who kept it in very good condition a year and a half ago, but just recently I have noticed that it makes (not always) a very loud motorcycle or souped up subaru like noise (almost like a very deep purr), when it is making this noise it uses a very large amount of gas and the car often needs more oil when it does this for too long. It doesnt always make this noise it can happen when I just start the car and may go away once I drive it for awhile or it can be fine when I start it and then start making the noise after driving a ways. Any ideas on what this problem may be and ways to fix it?