I would start with, what is the maintenance history of the car? At 154k there are some things that should have been done by now that could effect what you're describing (new plugs, valve adjustment, etc)
Car has 162k on it now.
I changed the plugs w new NGK and adjusted the valves myself at 105k.
O2 sensors are original.
It was about 80 degrees outside.
I didn't hear this noise at all on the 50 min drive back to the house.
Temp had dropped to like 60 by then.
Oil level is full. But this car does use about a quart every 1200 miles, especially doing 80 on the highway.