I can't believe I forgot to mention the model & year! Its been a rough month and not getting too much better very soon.
Yes, it's the 1987 944S. The tensioner is reasonably new, within the past 1500 - 2000 miles or so. Investigating the a noise after I bought it, we pulled the valve cover and checked the tensioner, chain, etc. Everything was fine but most of the spark plugs had managed to come halfway out. According to the service records that came with the car, the cam belt was replaced around the same time. I posted a detailed list of the various service records and work it had done on it prior to my taking possession of the car
right here.
Something I forgot to mention: During the recent arctic cold snap, I started the car and got a loud, high pitched squeal that went away in a minute or so. I chalked that up a frozen belt but it was also the first time that I had to really crank the starter to get the car to fire up since I've owned it. Every time I've started it since, I've gotten that squeal for various lengths of time. The engine hasn't fired up as soon as I turn the key since then. I drove the car a few times since that first difficulty it had starting. That was when I really noticed the clattering noise.
I did let the engine run for a while after adding the oil but maybe not as long as needed. I'll give that a try in the morning.