This morning I started to hear a strange noise when idling. I noticed if I changed to 'P'ark that it goes away. Only if in 'D'rive or 'R'everse.

The car idles perfectly, however when the problem occurs it's at regular intervals. I guess about every 2 seconds. Look at the RPMs it does show a dip, as I expect.

I have had the throttle unit replaced about 1.5 year ago, so I'm sure it's not that, or could it be?

Any ideas? Gearbox?

BTW, the gearbox is a reconditioned one, since the previous owner replaced the broken one.

 

Delighted to report, the problem did not happen again this morning. Holding thumbs that it was a once-off problem.