sat for a year now slight knock at idle??

[MYFREE95,240SX]

got my baby running this past weekend after a year of sitting and took her for a drive.. question for you, i got the car running no problem fired on first turn of key, but now has a little knock at idle. i did not change oil yet am doing that tomorrow but i did put a little oil into the motor and it has sufficient oil and it looks decent. any idea why it would have this slight knock now? could it be the older gas? there was like an eight of a tank sitting for prob around 1.5 years i added 5 gallons and a half bottle of fuel stabilizer any ideas as to where the knock came from? also alternator was putting out 18.2 volts when running. i assume that it was the voltage regulator was fried i ordered a new alternator. so any ideas?

[krash]

You should probably swap out that gas man, just to rule that out. How loud was the knock? Like rod knock loud?