Both previous posters are correct. Adding to Don's recommendation, however, what I would do is change oil and filter putting in Chevron Delo Multigrade 15W40. This is an oil developed for diesel service but with all the latest gas engine certifications as well. It has a dramatic amount of detergents in its blend but has a very strong base stock.

This approach is extremely safe because you are using a proven blend rather than an additive that may or may not be a good balance for your existing oil.

After running the Delo about 500 or 1000 miles, drain it while the engine is HOT! This will get the gunk out with the oil. If it is still ticking do this again. If you drive the car on short hops, you need to take a few trips at least 30 miles or so at speed to bring the oil to operating temperature to help loosen any contaminants and draw them into the oil so that they will come out with the oil when drained.

Good luck,