As you alluded to a blow off valve releases extra air when the throttle closes suddenly. More accurately, it releases extra pressure to prevent damage to the throttle or other components. An aftermarket blow off valve can make more noise or be necessary if other modifications allow for higher boost.

What you need to look for is engine codes or other problems. The blow off valve usually recirculates air into the turbo to prevent inaccurate readings on the mass air sensor. By venting to atmosphere the blow off valve makes loud noises but also releases air that the engine doesn’t know is missing, which can cause issues.

Try driving and suddenly letting off the throttle while under boost then quickly getting back on throttle. If the engine stutters or stumbles then the engine isn’t tuned for the aftermarket blow off valve, if it doesn’t have an issue getting back to power then it should be okay.