Does this sound like a bent chain ring ?

If it is rubbing on and off while you pedal, it is probably a bent chain ring, but if it is rubbing all the time, your derailleur is probably not properly aligned.

It sounds like the chain ring is off a little. If it's not too bad you can adjust the derailleur so it wont rub. You also want to make sure you are using the right combination of gears. Using the smallest chain ring on the front with the smallest gears in the rear can cause problems. The same thing goes with the largest in the front and back at the same time. I had a Walmart bike that would do the same thing and had to replace the chain rings before it would work right.

If you hit a rock or something with it, it may just be binding up and need some grease, which is causing it to jump as it is forced to bend tightly through the rear derailleur and gears. Take it off and make sure every link is equally loose and flexible. If you find the problem, and it's just one link, it's an easy fix to just remove it and ride with a slightly shorter chain. I hit a lot of rocks with my low bottom bracket, and have that problem a lot, and I usually can't spot it just by looking at the links.

I would think if the ring was bent, you could see it. Try taking the ring off and lying it on a flat surface. It's also possible that your crank is loose on the bottom bracket. If that's the case, you've probably already ruined the crank. If it only happens under power, it may be a flexing bottom bracket; which could mean either a cheap frame or a broken one.

it has to be bent

or you are pedaling so strongly at one point that you bend it temporarily

or it;s weak enough to do that anyway

a little bend isn;t necessarily bad

you didn;t say it caused any other problem

you can probably adjust the front derailleur so it won;t do that

either that or bend the derailleur cage slightly

it;s probably on just one gear right, and not the middle one?

wle.