On Saturday, 7 September 2019 16:01:01 UTC-4, AK wrote:
I recently had my rear derailleur replaced along with new shifters on a 18 speed mountain bike.

Shifting in the lower gears is smooth and there is no noise when pedaling..

I can shift smoothly into all gears however, there is a "clicking" sound when I am in the upper gears.

The bike tech who did the work said he could not find a seven speed shifter and installed an eight speed shifter and told me he would make adjustments so it would work.

I have been told this.

"It is a problem, but can be fixed by also replacing the freewheel, but I definitely wouldn't be paying for any service from a tech who didn't know this would be a problem."

https://imgur.com/a/xF73i91

https://imgur.com/a/5VB6gat

Are the shifters INDEX style? Are you using the shifters in Index mode? An 8-speed shifters in Index mode can shift an 7-speed cassette or freewheel because the cog thickness and spacing are so close in a 7-speed and an 8-speed system. However, in index mode a 7-speed or 8-speed shifter will not work properly with 6-speed cassette or freewheel because the cogs and spacers are thicker.

Is your chain or derailleur hitting the spoke protector?

How many gears do you get that "clicking sound" in?

Cheers