I've got V1.8 and it goes off all the time in the "A" mode. I 'spose you're not getting any repsonse in the other modes....sounds like that one needs to go in for service. I hope you bought it cheap and the S/N is still readable.
I had an earlier version, don't recall which version, but the newest models clearly have superior sensitivity and I don't think are really any better at filtering "false" alerts. The laser section appears better on V1.8 as well.
BTW, great detector but you probably already know that.
