NameTaken

Hello all.
A few weeks ago I noticed my bike was making some noises I hadn't noticed before while pedaling. I don't think it's chain rub as I did have some of that shortly after I purchased the bike and the LBS took care of it. Rather than explain it I mounted my action cam to the lower portion of my seat tube and did a short video. Maybe some one here can tell me what might be causing this.


A bit more info about the conditions. This is a Roam 3, all stock, with 3x8 drive train. I generally stay between 3 and 6 on the rear derailleur and the middle or big gear on the front. This was middle gear and 6 but I can hear this sound on all gear combinations. It gets significantly louder while pedaling hard. In the video I am going roughly 16-17 mph and it was windy. I stopped pedaling a few times to show that the sound is only while pedaling.

I did take it back to the LBS after it got it's tuneup a month ago and the guy rode it around the lot but didn't notice anything. He seemed to think it was due to the surface I was riding on. I have since removed my kickstand so the only thing mounted is my mini pump, bottle cage and a small bag under my seat. I really think there may be something messed up inside my crank set but I'm still very new to bicycle maintenance and thought I'd see what the forum thinks before I take it back to the shop.

Thanks in advance for any assistance you all have to offer.

Andrew R Stewart 

Sure sounds like chain rub to me. What on is the question. The chain might be contacting the cage insides,try slightly moving the ft shift lever to see if the cage being relocated will increase or decrease the rub. The der cage could be rubbing on a plastic ring guard. Carefully track the chain's pathway from many angles and see if the chain is touching anything besides the pulleys, the cassette and the rings. Try removing the chain from the crankset and spin the cranks. What happens? Are we to assume that the chain and cogs are not well worn? Andy.

bikeman715

I agree with Andrew , sounds like a chain rubbing on the cage .

NameTaken

Thanks for the input guys. I'll try to find some time to investigate further tomorrow. I paid for the lifetime service plan though so I'll probably take it in anyway. I don't mind learning but I'm still not confident enough that I won't mess something up trying to fix it myself.

u235

I didn't hear anything obvious out of the ordinary (assuming quality of the video and the wind). Maybe it's overall resonance or a vibration with the plastic chain guard? Sounds similar to my 3x8 setup on my hybrid but again, I've never filmed mine to directly compare what it sounds like on screen.

You don't have to try to adjust anything but this guide will show you what is involved and what to look for in the alignment of a front derailleur. Your current setup shifts fine so at least nothing is far out of whack.

Front Derailleur Adjustment | Park Tool

That guide looks like a lot but in reality, once familiar with what to look for, it only takes about 30 seconds to diagnose if a front derailleur is setup right. It can take longer to actually fix it though.

NameTaken

So I took the bike back up to the shop and believe it or not the thing was dead silent. The mechanic even rode it up the street a few blocks to see if he could hear anything. When he didn't hear anything he rode another bike and followed me for a few blocks and not a sound was present. I'm completely perplexed. He did oil my chain, tighten my spokes and adjust my brakes but he didn't think they would cause the sound I recorded in the video. He put it on a rack and looked for some chain rubbing but couldn't get it to do anything out of the ordinary. Even did some short sprints inside the shop and its as quiet as the day I bought it. I'm kind of at a loss really.

Andrew R Stewart 

This reinforces my speculation that the noise was chain rub. If it had been contacting the ft der cage then a simple trimming (or moving of the shift lever) might well relocate the cage and eliminate the rub. I have many customers who don't know about the real function of their shift levers or sometimes even if they have "done anything" when something changed. Andy

LaughingBasher

From what i see your sprocket isnt align with the bike so try tighten the crank nut or check whether the sprocket is bend



If no it might be the derailleur alignment youtube : how to Adjust a Front Derailleur

02Giant 

I stopped the video at a point where there was more sunlight in the image. I zoomed the video still to 300%. It looks like the chain is rubbing on the inside of the derailleur cage.

In Windows, control key and +/= key to zoom, control and -/_ to return to prior settings.

bikerjeje

Front derailleur chain rub is a common issue. Well, it's a great chance to learn how bike works. For your problem, usually it can be solved by turing the front derailleur barrel as it seems the rubbing is left side of the cage (which means it happens only with lower rear gears). If you want to set up nicely, google "How to Adjust a Front Derailleur" and look for the youtube video.
Anyway, I don't think the position is off if it has been working well. Perhaps, you can just turn the barrel adjustment until you don't hear rubbing. Once you don't hear rubbing, shift the rear gear to the smallest cog and try it again. If you don't hear rubbing, everything will be fine (assuming your front cog stays in the middle).