What makes you so certain that you have one? They are rare and usually aimed at high value targets. I recently read posts from professionals, that there has not been any appreciable activity in bios infecting proof of concepts, let alone real infection distribution campaigns.
Not trying to debate you, insult you, or otherwise antagonize you, so don't take umbrage. It is simply that your having one is about the least likely explanation. A software or hardware issue is much more likely than a rare bios rootkit.
No, don't think I have one just ran across this subject in conversation and was wondering what the possible effects would/could be. And how to fix it IF it did occur. I found a post elsewhere suggesting that indeed reflashing the bios would fix. Thanks.
The BIOS isn't the only firmware on a motherboard, and GPUs and storage devices have firmware too. A sophisticated enough rootkit could infect any or all of them, the only way to be sure is to throw it all away.