Am encountering intermittent, very loud noise that sounds like a baseball card in the spokes of a bicycle.

It only happens at highway speeds, i'd wager above 3500rpm, where i'm cruising at about 110km/h

if i let off the gas and coast for a while, it usually slowly gets quieter.
If the car gets parked for any amount of time, it gets quieter.

got it to happen down to idle and pulled over and tried the stethoscope.

the only place i could sort of hear it was on the fuel pump?

timing cover was quiet, as were all the points on the head i tried.
did not try distributor i don't think.


i'm beginning to suspect potentially it's a meshing/input shaft noise on the tranny.

It almost sounds vaguely reminiscent of a rod knock.

I do have oil pressure and good oil in there, so doubt it would be.

Anyone have any ideas?