I am getting a thumping/knocking feeling in the pedals when I pedal my Giant Rapid. Seems like maybe it's in the crank. Bad bearings? Anyone have an idea? It's not severe but it's getting annoying.

Could be a lot of things:

Poor derailleur adjustment.
Tight link in the chain.
Failing or loose bottom bracket.
Loose crank arm.
Bad pedal bearing.
Uneven or improperly mounted tire.
Wheel(s) out of true.

We need a lot more detail to diagnose this without seeing the bike. What is the frequency of the thump? Every pedal stroke? Less often, more often, etc.

Bring it by as BikeShop for personal attention .. (you are using the computer at work aren't you?)

Happens at same point on every pedal stroke, and only when pedaling, which should eliminate wheels, tires, and chain (?)

So it could still be several things including the bb bearings, cups not tight, arms not tight or a bad pedal. If you can't diagnose it further, fietbob's recommended visit to the LBS is a good idea.

Last issue I had with the ended up being a bad pedal, took them apart and greased them up and it sitll did it. I replaced the pedals and it was gone. Before you start digging around in major hardware give new pedals a try, even if it's just sliding some old platform pedals on to rule them out.

I'll definitely try new pedals, and tighten up anything in that area, thanks! Is it difficult to check for bad bearings?

I'm guessing the BB isn't going to thump because of the bearings...unless some fell out.... It might grind and pop some.

BB might thump if a cup came loose and it's sliding back and forth against the cup.

I'd be checking pedals and crank arms.

There should be no play in the bearings and it should feel smooth when turned.Any sandy or notchy feeling is not good.

If you can see the bearings,look for pretty blue and purple colors also scoring/pits in the balls and races.....either one is not good.

Last thumping on my bike was a loose pedal,took out my crank by the time I made back to town.Came loose after almost 3 years....What's up with that?

I hope you don't need to come off any time soon...said the RED Loctite to the new crank and pedals.

Not NEW pedals - overkill. Tighten pedals and crank arms, plus BB itself if it persists. In-person diagnosis by a shop or at a bike co-op is probably a good idea.

I had a similar situation. Mine was the axle had come loose from the spider on the drive side. Check for any sideways play in the crank. If there is "give" between the axle and the rest of the crank then unfortunately your crank may be shot like mine was.