1997 Chevy Tahoe ticking noises from engine

We bought a 1997 tahoe almost a year ago. We did a full service tune up. Prior to the tune up it was occasionally making noises in the engine. At first it was ticking, now it sounds more like a swish swish noise. Sometimes its there and other times is not noticeable. With the tune up we added a quart of lucas stabilizing oil (the mechanic said it might be sticky valves). It seemed to help for a while, but now is getting louder and more constant.



How do I fix it???? Please help.....