94 altima motor noise

I have a 94 Altima with a 157xxx miles on it. Approximately 1 week ago I noticed a very slight noise coming from it, at lower speeds (under 20mph) that sounded like it may have been an exhaust shield rattling. I didn't think anything of it & than yesterday the noise got much worse, to where I was able to hear it including when reving the motor & it sounded kinda like a rattle/tapping noise; so I decided to check the fluid levels & there was no oil on the dipstick. Had my dad run me down to autozone for I could get some oil. Took 2 quarts of oil to fill it up. After making sure it was filled up I than started it up & the noise was there, but after a couple seconds quited down. Now it still has just a minor rattling/tapping noise that seems to be coming from the passanger side of the valve cover area. Never had a problem with any oil leaks or noises like this before. Had an oil change done 3 months/2,700 miles ago, so its time for an oil change now anyway. I plan to get it in to the shop to get an oil change done, have them look to see if they can find an oil leak & where at & to see if they can find what the noise is. I'm looking to see if anyone else have questions on here, for I can try to keep from being ripped off by the shop, as all the repair shops here in my area have a reputation for lying out their teeth in order to get more money.

Thanks,
Tim

Turns out the problem is a dead lifter. Also have a major oil leak, along with transmission & power steering fluid leaks. The stablizer bar is also completely rusted. So I'm now just going to go ahead & get rid of the car.