Just a quick word of thanks to Mike, Marco and Laszlo for the advice. Interestingly I could find no mention of this using the in built 'help' feature. Its always simple when you know how!! Derrrrrrr!
I copied this from some other posting, in case u want to re-enable in future ...
Also, you can use the keys I and o to remove the yellow markers ... i alone works if you use it immediately after creating the loop, and you dragged right to create it. If you dragged left then it would be o that works alone. And if you've moved the cursor at all since creating the loop then you'll need both i and o.