sounds like it was wired wrong, but LED's up front will not fix it. I run front LED turn signals, and I had to wire in some large resistors to fool the flasher into thinking I had the stock bulbs still. Without it, they blinked at the speed of light!
The other day I removed one of my rear lights, to touch up some paint. After I put it back in, I noticed my turn signals were blinking rapidly again after driving around a few miles. The connection must have worked loose, and now without the rear bulb in place it alerted me to the problem. Of course this has nothing to do with your problem, as you say both blink at the same time. Something is wrong with the way the wires were run, yellow wires are for the left turn signals while green is for the right.
