Many of us work the digital modes like the various PSK's, Olivia, Hell, ect using a sound card interface of some sort. They work pretty darn good in transmit more, if you pay attention to your gain settings and the ALC level of your rig. I hear signals every now and again that are totally whacked out, and most of the time it turns out to be an over driven transmitter from the sound card audio.
I snapped this pic a couple nights ago while operating on 40m PSK31.
When the station in Cuba would transmit (his primary signal is on the
left in the waterfall), an image would appear abt 700hz up the band
(seen on the right in the waterfall). His signal sounded horrible, folks
were trying to get him to try turning his gain down, but I don't think
he understood what was going on. I'm not picking on him by any means,
but you do see a lot of this on the air. I suspect his digital interface
was over driving the bejesus out of his transmitter...