Spontaneous System Beep

We have a network with about 1000 users. Last week, 7 users from all different locations, different software, and different PC types, reported a random system beep that is loud when they click to minimize, maximize, and many other different times.

I have scanned for viruses and have removed all spyware. I wasn’t able to come up with anything. We have found a way to stop the beep by making an adjustment in Device Manager, but would like to know what is causing this.

All the users that have complained at this point are internet users. Anyone else have this problem with any info?