First off, new to the forum and looking forward to the vast information provided here.
I work for a telecom company and we often install paging systems for our customers. We use Valcom exclusively due to the ease of utilizing twisted pair cabling. That said, I recently replaced a Telecor 25 volt system with a Valcom Class Connections system. In addition to the existing 25 volt talkback and one way speakers we also installed several Valcom ceiling speakers for additional coverage in hallways. Everything was fine at first but now I'm getting a high pitched buzz through the one way 25 volt speakers and horns. It doesn't affect the one way Valcom speaker or the 25 volt talkback speakers. The one way 25 volt speakers and horns are powered by a 200 watt 2 channel amp to a 25 volt transformer and then to the speakers and horns. I thought I found the problem via a grounding issue as it went away for about 2 days but returned. This is a barely audible, (to a 64 year old installer) buzz but can be readily heard by the teenagers in the high school. I haven't isolated wiring yet but figure that's the next step. The original Telcor system either took a power hit or storm damage.
Thanks for any help!