I cbf to record myself humming it or something but it's a 2 note melody (with note B being the higher pitched) that goes
A B AAB AABA AB
Edit: I don't know if all the wildly different and incorrect replies are a bit, or if this post really is just that vague, but here it is hummed https://voca.ro/17WHcwM48PVa
I think this is it but I have absolutely no idea how I heard it since I never played any Mega Man games lol. I thought it was a Russian folk tune or something; maybe this is a tetris theme type situation??