The hydraulic lifters on my 90 Carat 2.1 have started making very loud
noises if the van sits for a few days.

I noticed when I drove it VERY heavily loaded with stuff to New York
(from Alabama) a few weeks ago. I pulled into a rest stop and heard the
clacking, so I slowed it down the rest of the trip. It was quite hot
those two days.

When I backed off on the highway speed, everything sounded good again.
I parked the van for a week in NYC. When the parking lot guy brought it
around, I heard the clacking again, which disappeared once the car
warmed up.

That was a few weeks back. I'm usually in it every day for something,
but I haven't been outside the home office for a couple of days.
Tonight, I went to the store and the clacking was back. Didn't drive it
far enough to make it quit altogether, but it did subside a bit.

What to do?

Thanks,

Jim