Usually when the chain is on the biggest gear, whenever I push the pedals too hard, i hear a "cracking" sound from the front gear. I am not sure how to describe the sound, it sounds kinda like the sound that comes from switching gears. It also happens when riding over bumps or potholes.
This is really annoying, since i can't pedal fast.
It would help a lot to know your crank brand and model and how many gears your bike has (to further narrow down your model).
The past few Shimano hollow drive-side crank arm generations are known to separate and they might crank first.
Try checking the chainring bolts. Sometimes these are located on the back side of the crank arm. They need to all be tight. There should be a light coating of grease on all the interfaces between the chainring, crank and bolts. If your chainring has ever been removed it’s likely it wasn’t greased properly. If I’m doubt, regrease and reassemble.
Other likely culprits are bad bearings in the pedals, bottom bracket, or rear hub. It could also be the cassette, free hub pawls, seat, seat post, frame, etc. There’s a near endless possible causes.
You really have to closely inspect the bike and do trial and error, eliminating as many potential root causes as possible. I would suggest removing your chain (from the chainring, it can stay on the bike) and trying to recreate the noise while standing on the pedals (hold onto a poll or doorway). If you can get it to make noise then, then the root cause is likely in the crank or bottom bracket or frame.
Even the saddle can creak in rhythm to heavy pedaling. You can test this by standing and seeing if the noise continues.
A different suggestion. You say it happens when going fast in top gear. The chain will be relatively unloaded by both your pedaling and the derailleur tension. It also happens when jarred by road irregularities. Likely the chain is slapping against the front derailleur, perhaps the top. You might be able to change things by removing a link (check your big/big combo of course).
