adtran alm light blinking

We have a point to point private ds1 line connecting two sites. In the building the line goes from the dmarc to the tsu, to the cisco router via v.35 cable. The site is up and running but I noticed that the alm light on the adtran tsu LT was blinking then it would go off for about 30 seconds, then blink off and on for about 15 seconds, and so on…..I looking into the status and yellow alarm was active.. What does this mean?