Working two GPX4500 close together

Hi All at GD&PF

Need help with working two GPX4500 close together, my mate and I both run 4500 with coiltek coils and have a lot of trouble when we get within 100 mts of each with interference noise,( I ask him to leave but doesn't work) and yet the others have 4000 and 5000 and we can get within 30mts of each other, tried lots of different things but still can’t get close, it is a real pain in the rear end when you are trying to work a small patch of ground any help would be good.
Many thanks
Yours in looking for (lots of ???) GOLD

have you both tuned your detectors.. tune yours first, then tune his after yours is finished.