Any cellular device sending or receiving texts will turn its transmitter on, which can cause interference with a sound system - this wouldn't be limited to androids. In fact you can get interference even without anything being received - phones periodically handshake with the basestations, and you can hear this too if you put one near a speaker (I often enough hear it on radio interviews, where presumably some interviewee thinks they are too important to turn their phone off for a few minutes). I would have thought it would be best to just keep radio transmitters away from sensitive sound equipment per se.
The bit about "containing a url" is interesting though. I can't see why that would make any difference at all with a text (and probably not a tweet), because it's just characters in a message. So if it really is different when a url is included, that sounds like someone has an app running which responds when a url is detected - maybe resending it somewhere, or possibly loading the link automatically (though that would be appallingly stupid from a security point of view!). Either way, that's not a standard part of Android, so if that's what's happening it's because of something that the user has installed on their phone.
