Strange text messages at five-minute intervals with no sender

So, I've been having this problem recently where I get these extremely strange text messages being sent to my phone. They have no sender associated with them and just look like a bunch of gibberish. Here is a screenshot: > Currently, I am getting the same message multiple times every 5 minutes. At first I just sort of ignored it, and one day I decided I would just go ahead and delete all the messages. As soon as I deleted them, they just kept on coming back at 5-minute intervals. I am on Sprint on the Nexus S 4G. My phone has also been doing other weird things lately. Sometimes when I lay it flat on a surface, it will just reboot itself constantly. I'm not sure if this is related to the text messages or not. Also, the messages only show up in the "Messaging" app which I don't really use. They don't show up in Google Voice at all. I actually got some of these weird messages about a month ago, however they stopped for a good while. Today, I just decided to delete them, and now they've been coming in every 5 minutes. So far I've received 32 in the span of about an hour. I have not talked to Sprint about this, and I don't believe I have been charged for them. Also, I can't reply back to these messages. If I try to reply and I hit "send", it just tells me that the message was not sent. Factory reset the phone. The messages are still coming in.