[Elecraft] Questio when using a Heil Proset

[Ross]

I have just received my K3 and have been using it on data, and it is working well,
But I have a problem, when trying to use the Heil Proset it receives ok but when I try to
use the PTT I get a loud audio noise over the top of my speech, it sounds like someone
giving a loud "raspberry".
Trying the MH2 hand mic everything works perfectly, there is no noise and using the monitor,
my speech sounds normal. 
The problem with the Proset also occurs if I try and turn on the K3 manually.

Ideas please, what have I set up incorrectly, or is it the headset?

Regards to all
Ross
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