The engine light comes on and then goes away

hey guys, i got really concerned after doodad's engine blew. I was very sorry to hear that. I thought maybe i i should bring my problem up too. Everytime i start my car, i see this engine oil light and after a few minutes (3-4) it goes away and everything is fine. Even when the light is on, the car runs fine, meaning the light doesnt make a difference in terms of the car's performance.
The weird part is that i changed my oil four months ago and i have approximately put on 2500miles on it. What could cause the engine light to come up? More engine oil than i need?
2nd prob = this has been mentioned in other threads but i want to explain it, just to make sure that this has nothing to do with the engine oil light. When i start the car the oil light comes on and i hear this knocking sound, when i accelerate it gets faster and therefore has to do with the engine. Lot of people have written that its a piston slap.
Any help on these two issues would be greatly appreciated! Thank you very much.

The oil light comes on in the event of critically low pressure. And startup is when the most damage to a engine occurs due to lack of said pressure. Your knock is not piston slap by far, it's dry bearings that are not going to take much more of the abuse.

Now, this started occuring just after you changed the oil? What grade & manufacturer oil did you use? How much did you put in? How much is in it now? Did you replace the filter? Again, from who?

I had the oil changed by a mechanic and i do not know the company name of the filter manufacturer. I think most likely non senthytic oil was used. I checked the oil level yesterday and its a little more than full. I got the oil changed 4 months ago and i put 2500miles on it. I think they might have overflown or added more oil than i needed. This started occuring after a couple weeks and i thought they might have just put more oil. Thanks

Well it's in your best interest to take it to someone you can trust and have it changed again, pronto, if you can't do it yourself.

After how many miles does the oil needs to be changed?

i change mine after 3k or 4 months. sometimes sooner if i've got extra cash. its the easiest and one of the most effective ways to keep that motor runnin longer.
:)
anyhow, you better get that damn thing to an oil change pronto, or hook up a codescanner and see if your car is throwing any malfunction codes.
Local autoshops usually do it for free. Try to not drive it long nor hard while its knocking. As said before its not standard ls1 piston slap. its very serious ;)

thanx a lot pal :D. tmrow is the oil change day.

I just got the oil change done and the car is better than ever :D. Engine oil light comes up nomore either. Thanks a bunch for help.