How much brake booster/actuator noise is normal after a new unit is installed

I had a shop (I will not name) install a brake booster yesterday. I picked the car up today and I found out that instead of installing a new unit they put a used one in. This was never discussed and I assumed I was getting a new part. I’ve driven for the last year with various noises and lights on the dash. The idea of putting in a used unit and potentially going through all of this hassle again makes me sick.

Anyway, lights are off on the dash, I have proper pedal feel, but the buzzing when pressing the brakes seems like it is happening a lot more than I remember a healthy car doing. I can’t remember how much buzz you should get. With this “new” used unit it happens with every press of the pedal and continues every 30 seconds while holding the pedal down. My defective one would buzz even when not pressing. This used unknown mileage part is really annoying the hell out of me. What is normal sound for a brand new unit?

The owner and mechanics at the shop seem like good guys. I just need them to make this right. I would have never authorized a used unit, which would have me wondering if and when it will fail again. Mechanic tells me they always put used ones in. Owner told me he was going to “order the parts” and never indicated USED. This probably happens at a lot of places but there is no way in hell I want a used part in, especially when I was not told about it when given the quote.

Please let me know how much buzzing I should hear? every press along with multiple buzzes while holding pedal seems like this used one is worn. What’s the general consensus.