[VHFcontesting] DEMI VHFLNA 2M preamp puzzle

[Chet, N8RA]

I thought this preamp was working OK for a few months, but it is not now. 
 
When it is out of its die-cast box, it seems to hear and tune up just fine.
But when I put it back into its box, it still outputs a higher level of
background noise, but the input signals are not amplified. 
If I just crack the lid a bit, it again hears OK, but when completely shut
it does not. 
 
Input detuning? But there is not way to tune it when it is in the box.
 
Any ideas??
 
Chet, N8RA