Good afternoon expo lovers. I own a 2003 5.4 triton Eddie Bauer expo. Thing is solid and had been in the family since 2010. The other day I come outside from work and start it up drive off, and start hearing a tapping noise. First thing I say oh goodness not a valve tap. Then I listen even even closer and it goes away. Then it comes back at certain point of driving home. Weird. What do you guys think 285k on it. Regular oil changes, stays with Motorcraft oil along with Lucas. Any tips?