Chain rubbing against cassette cog, please help
 

I have been getting intermittent little noise and clicking sensation from the pedal lately(specially in lower/heavier gear and when putting more torque).
I cleaned and inspected the bike and found out that my chain is rubbing against the second cassette cog (when it's in the first cog).
Gear Position: front - biggest(heaviest) gear / rear - smallest(heaviest) gear (it's road bike - giant SCR 2 claris 8 speed)

I tried adjusting the barrel adjuster, limit screw and the cable to move the rear derailleur to the right most side(outward) so that the chain will not touch the cog.
However, the chain is still rubbing the cog.

I have replaced the chain and sprocket cassette about 2 month ago and rode good 1,000 km without any issue.
I just started to have this issue recently.
Which area should I fix or inspect more?

Any advice will be greatly appreciated.

Thank you.

Apparently, i can't upload pictures......
Just to clarify the point of contact: top side of the chain rubs against second cassette cog.

First thing I would do: Check to make sure that the cassette lockring is tight

Yes sir, it's as tight as teenager's *****.

Don’t be gross.

This question should be posted in the proper section...bicycle mechanics...not GD. And show some class OP.

Is the right speed chain being used?

As a chain wears down, it will start flexing more to the sides which may cause it to start rubbing the cog next to it.

Solutions:
- Measure the chain for stretch with chain stretch tool or straight rule. If stretched beyond acceptable parameters, replace chain.
- Avoid "cross-chaining". Avoid shifting to the outermost cog of the cassette while the chain is on the smaller, inner chainring. If you have 1x drivetrain, move your chainring outside of the crank arms so it becomes more aligned to the outermost cassette cogs.
- Get better quality chain next time with less sideways flex. Lower quality chains tends to flex more to the sides and may result to slow or delayed shifting between cogs. More flex will also make chain more likely to rub against adjacent cogs.

9 times out of 10, chain rub like this is caused by a bent derailleur hanger.

Check the rear derailleur hanger alignment, both axes (top-down, front-back).

Either take the bike to a decent shop, or buy an alignment gauge. They're not expensive.

FTFY. Chains don't stretch, they WEAR. No need to avoid 'cross chaining, every modern (the last 20 or so years) can do it. Small/small isn't a great idea, big/big should be no big deal. You don't want to do it all day, but using that combination is fine.

Horror of horrors. Yesterday I was climbing a short hill using my big ring. This hill gets progressively harder towards the top. Normally, I can get there on my big ring using the third largest cog but this time I was tired and it was very hot so I committed a terrible sin, I shifted into the largest rear cog while on the big ring for the last 20 meters of the climb.
The world did not come to an end, I finished the climb and shifted back to a "safe" gear combination

That is extremely weird. If what you report is true, you have a really messed up chain line.

Something doesn't add up.

Unless you were one of those guys on here lately who refuses to size the chain to do big/big because "I never use that combination" right up until they do.

No way that is happening.
^This^ That's just not possible.

I know that. Chains wear, they don't undergo elastic deformation unless you rode your bike over molten lava or you ~leased~ it to an actual gorilla that can ride a bike for 5 mins while carrying a golf club in one hand while hopping curbs but I'll call it whatever I want to. Perhaps, I should start calling it "chain gellatffhfoourinnusous"

The OP's chain is obviously not doing well or the chain itself is flexing sideways excessively. Excessive sideways flex is a symptom of cheap chains especially if the chain is new or the chain for some reason is wearing at an incredible rate (OP must be riding over diamond sand dunes while using wet lube, what an awful situation to be in)

Gear spacing on a cassette should be sufficient to prevent the chain rubbing on the next gear - unless you're using the wrong chain. For instance, a 7-speed chain on a 9-speed cassette. Or a 5-speed chain on a 7-speed cassette.

OMG ! You now have to live with the shame ! :D