Does it feel smooth as you pedal ?
First port if call would be cranks and BB for me.
Make sure nothing is rubbing, chainrings, crank arms etc.
Does it have a sealed BB or is it an older style solid axle, bearings and adjustable cups ?
Either way, id squirt a bit of oil into the BB, turn the bike on its side and let it run down the side if the axle into the bearings, see if you can get it to quieten down. Its not a fix but can help you identify the problem area.
If that quietens it, new BB in all probability.
It could be pedal bearings but thats a heck of a noise for that.