Have a 2000 Crown Vic with 83K miles. Driving today and after a few miles I started to get an intermittent, but constant, audio tone coming from around the digital HVAC control panel. They has never happened before. The tone is not mechanical.

I though it was the radio. No. Then my cell phone, no. I turned off the HVAC control and the tone stopped. Turned it back on and it started a few miles later. Turned it off and the tone stopped. Kept it off and the tone started again-- even with the HVAC controls in the off position. All heat, AC, vent, temperature adjustment and outside temp controls work as the should.

Just for kicks, I stopped by my dealer and asked them. They had no clue-- other than the HVAC control module was going bad.

Does anyone have any idea what's going on. Could it be a vacuum leak?

 

Many strange sounds come from cars these days.
A vacuum leak is a good possibility. If it is , does the noise continue after you shut down the engine since there is a vacuum reservoir to empty? You will need some help from gentlemen on this forum with lots more experience on 2000 Crown Vics than I have.