Flashing Check Engine light, no code

Previously I had P0300, P0301, and P0304 come up while driving on the highway. Replaced spark plugs, didn't fix it, replaced wires from plugs to coil pack, no fix. Replaced coil pack, now the check engine light comes on but no code. Light comes on multiple times a day. Mechanic doesn't know what's wrong. Any suggestions as to next steps?

2007 Aveo LT

Edit - A couple months before this happened my computer went so I had to replace it and get it reprogrammed, could it have been programmed wrong and causing a faulty CEL? There is also a whining noise when I accelerate, not sure if related but I want to include as much info as I can

That is pretty odd. I guess I'd try disconnecting the battery for a minute to clear any codes. See what happens and if it comes back.