1998 Astro - 82K - tapping

Hi,
I was wondering if you might have some suggestions.

My Astro started tapping last night when I got home from work. It was running fine when I shut it down and I did not notice any tapping. I went out about an hour later to run my daughter to a doctors appointment and when I started it up. Tick, tick, tick. Very loud.

I checked the oil, it's not due for a change and the level is good from the last oil change. It's due for a change in about 1500 miles. Oil pressure is good. Coolant level is good.

background. Over the last couple of years the van has had several episodes if running ruff. Ultimately I had a full tuneup done and the wires replaced and she ran like a champ for about a year or so. Over the past several months it has started to do something strange. When I start it up in the morning it runs great. I take out and get about a mile or two down the road and it will start to miss. It will miss for about 1 minutes or so, than straighten out and run fine. About a month ago while I was driving it to work I the service engine soon light came on. I put it in the shop and they ended up replacing #3 plug. That took care of the problem. (For then). Yesterday on the way to work I noticed the old problem creeping back in. Not as bad this time but a definite miss.

NOW the tap. Tap. Tap.

Any suggestions?

Thanks