Drivetrain indexing adjustment and wear
Many noises and vibrations are amplified by the conditions in which we're riding inside, and so any imperfections in the bike - trainer interface are more apparent.
Rear derailleur adjustment
It is possible for your rear derailleur to be adjusted perfectly on your outdoor wheel and to be out of position by between 1-2 mm relative to the cassette on the trainer. If you're using a Zwift Cog, skip this section and continue below.
One easy way to see if your derailleur is out of position is to shift into the middle of your cassette and look at your bike from directly behind the trainer.
The pulley wheel closest to the cassette cog should be directly underneath (and in line with) the cog the chain is sitting on. If it's not, you can make small adjustments to its position. For a number of users, a few quarter turns of the rear derailleur barrel adjuster will resolve the issue. We suggest writing down the how many quarter turns you did, so that that you can undo them when you put your bike back on your outdoor wheel.
A more complete presentation of rear derailleur adjustment can be found in Park Tool's Rear Derailleur Adjustment article. If more than a few turns of the barrel adjuster (or micro adjustments of your electronic rear derailleur) are required, we suggest getting help from a bike friend or local bike shop in confirming the proper adjustment of your rear derailleur.
Aligning your chain with a Zwift Cog
Using your bike with a Zwift Cog shouldn't require any rear derailleur indexing adjustment. You do, however, need to ensure that you are shifted into your small chain ring up front and into the rear derailleur position that most closely aligns with the Zwift cog. In most cases, this will be 4-5 gears from your easiest gear. The upper pulley of the rear derailleur should sit in a vertical line with the Zwift cog when shifted into the right position.
Drivetrain cleanliness and wear
An overly dry chain is an apparent source of noise, as the metal surfaces of the chain rub against the chainrings and cassette. Likewise, an overlubrication or dirty drivetrain is a loud drivetrain, as the debris that accumulates in chain lubricant grinds the metal surfaces, making quite a bit of noise when there isn't road noise to cover it up. If you haven't degreased your drivetrain and relubricated your chain lately, it can be a great time to do some care and feeding.
Like everything else, drivetrains wear down over time. This wear allows for slop in the system and results in less precision and more noise. Particularly, running an increasingly worn chain on a new cassette can be very loud. If you don't know how worn your chain is, your local bike shop can check for you with a simple tool. In a similar way, a brand new cassette, with fresh cut teeth can be quite noisy at the start. If you know your chain is in good shape and the rear derailleur is well-adjusted, giving a new cassette a few weeks of riding to break in can resolve the noise.
If your concern is unresolved or you have questions, please submit a support request and our support team will be happy to assist you further.