I am getting quite a hissing noise in what I assume is the evaporator - when the system cycles on and off - is that normal?

The system was converted to 134a before I bought it. I recently had a new condenser, rec/dryer and exp valve installed professionally. And it's cooling nicely.

Just wondering about the hissing...sort of annoying to my ears.

__________________
DS
2010 CL550 - Heaven help me but it's beautiful
87 300D a labor of love
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Las Vegas NV