[S.J.SLEEPER]

I had a 00 v6 camaro that did that. I bought it with the lifter noise for cheap.
I used a old school trick my father-in-law told me about years ago.

1.Dumped oil out
2.filled it with 5qts. of transmission fluid
3. ran it for about 3-4 hours outside with a occasional rev here and there.
4.dumped oil, installed new filter & 10w40
5.noise gone....fixed & never came back.

Transmission fluid is a "detergent" oil. it will clean out alot of the nasty sludge or build up.
When you dump the trans fluid out the oil will be black as night.

Not guarranteeing it to work for you, but it has worked for me several times with noisy lifters. Its worth a try for the $25 you'll spend.