Autocom with a noisy lid (Roof V8)

I bought an autocom spa kit recently from here, ive installed it to my bike etc and to my Roof Boxer V8 lid, work fine at low speed but 70mph on the motorway and the vox kicks in with white noise, I have vox setting at least sensitive, air hole taped and I've tried fitting a chin cover to reduce wind blast, all to no avail, is my lid just too noisy? Any tips greatly appreciated.