Question about the Hayward BART station

Ok this is kind of an odd question, but:

A few years ago, whenever I went to the Hayward BART station (and I think some of the others) there would be this super high-pitched pinging noise going on all the time that drove me crazy. I think it was to keep birds and loiterers away. After a while, I moved to another city and didn't use BART anymore. Recently, I went back and I no longer hear the pinging noise. I'm not sure if it's because they stopped or becasue my hearing has become damaged enough that I can no longer hear that frequency. Has anyone else noticed the pinging sounds in the past, and is it still there?