Important to diagnosis: Without a fan controller, does the fan speed ramp up slowly after a cold start, or does the fan go full speed as soon as you start from cold?
If the latter, that suggests that a temp sensor somewhere inside the compeer was damaged during the drive swap. If that the case, a new logic board may be required and the the servce provider who did the work make it right.
Also, if a damaged sensor, a fan control app may not overcome that. Apple Diagnostics will pick up a failed temp sensor.
Use Apple Diagnostics to test your Mac - Apple Support
If that throws a code, there is a link at the end of that article to list of codes and their meaings.
Default fan speed on my 2017 iMac is 1200 rpm.