Does anyone know what might cause this, (attached audio file)

I was having this on my node, using a GE Mastr II with URI and DSP to decode the PL tone

123.0 - my first thought was feedback loop from the TX but it just happens without anyone keying up or an ID occurring. 

However also considered someone jamming / txing a near dead carrier with a hum on their signal. 

Tried reboot, and this would happen whether I was connected or not, it also has the courtesy tone, which is the local tone, as if it was a station here (local).

Changed the PL lower in freq and it all cleared up. Not sure what could have caused it though?

As far as I know nothing has changed at the repeater site, haven't been up there in ~ 2 months since the last change where I raised the antenna, from 10 to 30' and brought it about 15' closer to the repeater. 

If anyone has a thought other then some station keying up to cause this, jamming etc... what else could happen to do that?

73's

Mark KC7DMF