I have a strange tap. It's sounds like a normal valve tap except it taps a few times stops then taps again. Like tap tap tap tap nothing tap tap tap tap. It's on time constantly by that I mean the sound and silence are the same duration every time. It also taps constantly until it warms up. Not sure what's going on as this started about 3 weeks ago. Any ideas?? It's a 4.0 93. I am worried that I will need a new head soon. Hopefully it's a simple fix. Never heard a tap that stopped and started like this. Especially where it stays in time. Oil level is fine and I did an oil change. No difference.