I have this exact same problem! I explained my problem in extreme detail in this thread I created but just got the same non-sense responses that you are getting.

My spoiler also only works when driving at 65mph it doesn't work when pushing the button, I think it's related.

There is obviously something wrong causing this, and I bet there are more cars out there beeping at the driver all day long too. Car is not a primary driver and I've been moving slow.