I would guess that whatever equipment you have plugged into the T1 could potentially be doing that, but if you're not running a T1 with an integrated DSU (WIC-1DSU-T1?), I would suspect the external equipment.
I'm a bit curious though, the way you phrased it made me think that this is two T1's from the same internet provider. If so, who was it that called you? The internet provider or the local telco? I would think that if the internet provider called you, that he/she should call whoever provided their local loop, the odds of your equipment putting voltage on the line that would reach a provider at the other end are pretty much nil IMO. It would probably go through several fiber-optic lines before it reached the end.
However, if it was the provider of your local loop, you should coordinate with them to figure out what the problem is. Does it exist on both T1's, or just one?
The only time I have seen problems like this is when you have a bad ground with your equipment which can lead to a 50+ voltage on the line. One way to check is to use a power meter on the cable to ground. Or grap an o-scope and look at the signal coming out of your equipment, you will the smaller 3 volt T1 signal and the 50 AC wave on top of that. Just one thing to check.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...