Gearbox noises

[Trixibell]

Ok so I was stuck in traffic. Starting. Stopping. Starting. Stopping. All of a sudden I'm sitting in 1st and the car sounds like very loud grating/drilling noise. I took it out of 1st and it went away. Back into 1st it made the noise. Moved forward after about 30seconds it went off. Started putting it in neutral instead of sitting in 1st and it came back. Very intermittent. Only started today. Help!!
gearbox was changed when I bought it as I had issues with 3rd and 4th. So got a lower mileage gearbox and put it in...

thanks in advance guys.
Trixi