Engine tick/tapping noise only taking off in gear

[GregT]

The frequency will tell you if it's a valve. If it goes away when it warms up, you might have a valve in it's guide that is becoming loose, but when hot, seals up. I don't think I'd sweat it until it gets louder, or something affects the performance. the only way to make sure about tics like that is to do the head, and that may be premature, especially if it goes away.

It seems to be a low frequency tick which I think happens as the bike moves in gear ? Is this correct ?

If it is, I'd look at the output shaft bearing next to the final drive sprocket. It may be on the point of collapse. Pull the chain and sprocket and spin the shaft by hand. Any noise or if the shaft can be moved up or down and there's your problem.