Wallonthefloor

When I am pedaling my hybrid with a lot of torque no matter what gear I'm in whether it is climbing a hill or pedaling down one in the hardest gear, whenever I go over a rough bumpy surface my chain makes a very instant "ping" noise. It does not fall off the gear and skip terribly at least I don't think, it is like one quick and instant skip and it can be very consistent when applying force to the pedals and riding over some rough terrain.

I did just get a brand new drivetrain (new cassette and chain) at 2 different bike shops. At the first shop when I got a new chain the mechanic said that my derailleur hanger needed adjusted so he also fixed that. On a different day I went to another lbs to get a cassette because I realized mine was definitely at the end of its life and the mechanic changed it but after it was put on it had too much play. He immediately noticed, took it off and said that it needed a spacer. I told him that when I bought my wheels from the other shop that they told me never to forget the spacer because my wheels are 8/10 speed compatible so I would need it. He did not find the exact spacer that it came with but said he had a box full of them and that they are all the same so he put one on significantly reducing the looseness of the cassette. I have no idea whats going on with my bike, it shifts fine, I just don't feel the stability anymore while pedaling over any surprise terrain changes.

Wheels: Shimano Wh RS-11
Cassette: 8 Speed Shimano
Chain: KMC
Bike: Giant FCR3 (aluminum)

JonathanGennick 

Are your rings in good shape? I worked on a bike once for which it wasn't enough to replace cassette and chain. I had to also put on fresh rings to eliminate the skipping.

FastJake

It's hard for me to gauge how bad this is for you, but any derailer drivetrain is going to exhibit this to some extent. Since the rear derailer's spring tension is holding the chain in place, if you hit a bump it can throw that out of whack momentarily. Your bike (I'm assuming here) doesn't have suspension like a car so you have to go over the bumps smoothly yourself. You can't just slam into them and expect everything to be fine. The only way to truly eliminate this problem is to switch to a bike without a rear derailer, i.e. fixed gear/single speed/internal gear hub.

How much air do you put in your tires? Inflating them too much can cause unnecessary bouncing over bumps.

ThermionicScott 

Sounds like garden-variety chain slap to me. No big deal (at least on the metal frames I deal with ), but can be minimized by making sure you're in the largest reasonable chainring and cog combination for the gear you want -- that puts the chain higher up from the chainstay.

FastJake

If it's just chain slap, I find wrapping the chain stay with a cut up tube will reduce the noise and protect the paint at the same time. This is especially relevant on mountain and cyclocross bikes that live a rougher life.

Retro Grouch 

That's what your symptoms sound like to me too.

Try wrapping an old inner tube around your chainstay and going for a rough road ride. If the noise disappears, you've identified the problem. You can leave the inner tube in place, you can use something a little fancier to protect your chainstay or you can decide to live with it as it is.