Explosion-like sounds while starting the car. What to do? (Nissan Tsuru)

[timon_and_pumbaa]

Hello. For a period of time I haven't used my car in a while (more than a year). I know that this can be bad for its engine, and so recently I began starting it every weekend for a few minutes (it's unused otherwise), but the problem is that when starting, an explosion-like sound is heard. It's not very strong, and the engine starts usually after the second attempt, but I'm afraid that my engine can be damaged by this. The car is a Nissan Tsuru (From what I see in Internet, it's sold in other parts of the world as “Sentra”). What's the cause of this sound and what must I do? I should take it to the mechanic, but I want to have an idea of what the problem may be in advance to avoid being scammed and to know more about my car. If anybody can give an explanation of a possible cause please do. I'm interested in a technical explanation so please don't avoid technical terms. Thanks you very much in advance!.

[Crvett69]

can you tell what area of the car sounds is coming from, front, middle, rear? also if you can, drive the car up and down the street some to keep tranny clutch and brakes working right and you should let it run at least till temp gauge reads normal

[DeltaP]

What year is it? Is it carburated or fuel injected?