Once I reread your post, it sounds like a lighter noise ( aka lifter tick). Even an exhaust leak at the manifold can make a similar noise.

If thats the case, you might just need a new lash adjuster. Another possibility is you have air getting in them from a bad oil filter drain back valve. I have had good results running Purolater filters ( I get them off of E Bay) and 10W 40 oil . Since I run a turbo, I have been using Mobil 1. The 10w-40 high millage and the 0w-40 both work pretty well. For hot weather I have also run the 15W-50. That might be a bit thicker than you need, a high quality xxW-40 might not be a bad call.

At the very least, I would try a new filter.



Mobil 1 Oil Guide